:Maybe better to ask this at the [[WP:Reference_desk/Computing|Computing Desk]]. - [[User:Lindert|Lindert]] ([[User talk:Lindert|talk]]) 14:39, 11 January 2013 (UTC)
:Maybe better to ask this at the [[WP:Reference_desk/Computing|Computing Desk]]. - [[User:Lindert|Lindert]] ([[User talk:Lindert|talk]]) 14:39, 11 January 2013 (UTC)
:: Computing people probably don't deal with ImageJ. ImageJ is an NIH application. [[Special:Contributions/72.229.155.79|72.229.155.79]] ([[User talk:72.229.155.79|talk]]) 19:21, 11 January 2013 (UTC)
== is Asian male facial hair easier to wax than Caucasian facial hair? ==
== is Asian male facial hair easier to wax than Caucasian facial hair? ==
Revision as of 19:21, 11 January 2013
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
In reference to the premise behind the manner in which choke holds are effective, I find it difficult to understand how a chokehold such as the rear naked choke can "immediately deprive the brain of oxygen" ("safe application" section) if the vertebral arteries continue to supply blood to the Circle of Willis. I can hear that there's not enough blood flow, and so perhaps there's not enough oxygen for the victim of the choke hold to continue normal function, but to say that the brain is "immediately deprived of oxygen" suggests that there is no oxygen supply. DRosenbach(Talk | Contribs)06:13, 7 January 2013 (UTC)[reply]
According to my Chambers Dictionary (1979), the meaning of "deprived" is as follows: to dispossess; to keep out of enjoyment; to remove (as in remove from office). According to http://www.thefreedictionary.com/depriveit means to prevent from possessing or enjoying; to keep from possessing or enjoying; to remove from rank or office. It seems that DRosenbach is correct and StuRat is wrong (again). Wickwack 120.145.140.205 (talk) 07:09, 7 January 2013 (UTC)[reply]
That definition doesn't say to "TOTALLY prevent from possessing or enjoying", you just made that part up. See relative deprivation. You can't have a relative amount of an absolute, that makes no sense: "To relatively TOTALLY prevent from possessing or enjoying". A common phrase is a "deprived childhood", which means they had fewer material goods as a child, not none (they would have died in short order without any food, for example). Another common use is in the phrase sleep deprivation, which just means not enough sleep, not no sleep. Here's another example: "Excessive homework deprives children of time with their families" [1]. Obviously, this doesn't mean they don't see their families at all. And sensory deprivation, as our article states, includes a "reduction" in stimuli. Here are synonyms for "abridge" (meaning to reduce) which includes "deprive of": [2].
So, once again, Wickwack, in a blind attempt to attack me, you didn't bother checking your facts and sources first, made me waste my time to prove your wrong, and the time of everyone else who reads your incorrect comments. StuRat (talk) 07:36, 7 January 2013 (UTC)[reply]
I agree with StuRat on the 'deprivation' thing. However it seems to me all of these are somewhat approaching this from the wrong way anyway. We're talking about medical usage. If you check out Cerebral hypoxia and Hypoxia (medical), it's clear being deprived of oxygen doesn't mean completely deprived. If you don't like wikipedia, you could easily find other sources with the same usage. As the first article attest, particularly when it comes to the brain being deprived of oxygen even if it's only temporary and incomplete can have fairly bad effects. Nil Einne (talk) 09:04, 7 January 2013 (UTC)[reply]
.
Here again we see StuRat come back when he has been refuted - he can't accept being disagreed with and can get quite ridiculous and silly. Silly because he tries to defend what was initially just a simple human mistake. If his time has been wasted then that is his choice alone - I neither requested nor forced a response from him. His comment about me not bothering to check my facts is bizare considering that I directly quoted from a highly regarded dictionary (Chambers) and backed it up with an online link. I also checked some other dictionaries but did not mention them as there was no difference.
I cannot see why StuRat linked to the relative deprivation article (Relative deprivation is the experience of being deprived of something to which one believes oneself to be entitled) as this is both a technical term and a completely different concept - "relative" used in the context of relating to reality. — Preceding unsigned comment added by 124.182.3.218 (talk) 11:52, 7 January 2013 (UTC)[reply]
However, as it is known that Wikipedia is read by folk whose first language is not English, I feel it is worth while to show why DRosenbach is correct and StuRat is wrong. Here's the relavent principles:-
1. As I said before, the dictionary meaning is dispossess, remove, keep out/from, and the like. These are all or nothing words.
2. DRosenbach is correct in that blood flow in the circumstances of the article is not completely cut off, therefore the word "deprive" has been used incorrectly. It was used incorrectly as because of it a reader can validly (under the rules of English) take it to mean total cutoff of oxygen, just as DRosenbach said. Even if you accept that partial cuttof is a valid interpretation, it is still not good English as then there are two interpretations when there should be only one.
3. Expressions like "Excessive homework deprives children of time with their families" is not particularly good English, but is a use different to the use DRosenbach cited and never the less is valid because time is not a singlular non-divisble object. A portion of the child's family time has been taken away, not all the family time and this is clearly what is meant. In contrast, the expression "immediately deprive the brain of oxygen" is validly understood to be total loss of oxygen.
Let's say you have a 3 x 45 mm steel nail. I can either take it from you wholely, or leave you with it in its' entirety. I cannot, not without cutting tools anyway, merely reduce your possession of this nail. It is appropriate to write "Wickwack deprived StuRat of his nail" and it means Stu lost his nail completely.
Let's say I reduce the water pressure to Stu's house. It is NOT valid to say "I have deprived StuRat of water" - he still has water. We could say, if Stu then has problems resulting from the low pressure, "Wickwack has deprived StuRat of his enjoyment of water", or (better) "Wickwack has deprived StuRat of full water pressure." See the difference?
It is quite valid to write "It deprives the brain of adequate oxygen" (which is how the articles cited by Nil Einne start off), but not valid to write "It deprives the brain of oxygen", unless the brain is totally cut off from oxygen. See the difference?
4. The word "deprived" may get some common use in a partial effect context, as do many expressions in common informal and spoken use. But in things like encyclopedias, wikipedia articles, scientific papers, etc, the correct dictionary meanings should be used. Otherwise, readers may be confused, as the non-verbal clues in human communication are not available. For example teenagers these days say "Cool" to mean "That's good", "I like it", "Thank you" and similar. In earlier days teenagers used the word "gas" in a similar way (as in "It's a gas!"). Both, in theory, are a misuse as neither word means "good". However, they have become common use, so it's ok to use in speech and informal writing. But not in formal writing.
Actually it seems clear from the articles I cited the meaning is unclear whatever you say the dictionary says. Hence why for clarity both articles always make it clear whether or not they are talking about complete or total deprivation of oxygen rather then just assuming people will follow the definition used in some dictionaries and complicated technical arguments about what the word should mean in the context. Nil Einne (talk) 13:02, 7 January 2013 (UTC)[reply]
Purely original research, but I used to do a bit of Judo and have been on the wrong end of this hold a couple of times. My memory is that you are still able to breathe, but after a few seconds a large black patch appears in your vision and you realise that it's time to tap for a submission before loss of conciousness becomes an issue. I'll leave you to argue over the wording. Alansplodge (talk) 13:13, 7 January 2013 (UTC)[reply]
From what I understand of the various articles on choking, there are two main types of choking described:
Blood choking
Air choking
The choking I was referring to, such as the rear naked choke, is described as a blood choke, in that the vessels supplying the brain with oxygenated blood are actively blocked by the position of the attacker's upper and lower arm, while the trachea is left patent within the crook (inner concavity of the elbow) of the attacker's arm. The point being, I believe, that the trachea remains unharmed (if it were crushed in the hold, permanent damage would ensue) and the victim is able to breathe normally -- the unconsciousness occurs not because the victim ceases to take oxygen into his or her lungs, but because the oxygen that diffuses into the victim's blood in the lungs is not able to get to the brain. DRosenbach(Talk | Contribs)01:47, 8 January 2013 (UTC)[reply]
Quite so. However, blood flow to/from the brain is not cut off completely. If it were, it would be the same as cardiac arrest - unconsciousness would occur within 2 seconds or less. See also Wnt's comment below. It's not just a matter of obstructing the flow though. The sensors for blood pressure are in the neck arteries - applying external pressure tricks the brain into thinking blood pressure is way too high and it instructs the heart via the parasympathetic system (vagus nerve) to bring it down. It's the commanded drop in pressure that causes blackening vision and fainting as much as the obstruction, though the pressure drop in the brain is not as great as it is in the body. See http://www.cliffsnotes.com/study_guide/Control-of-Blood-Pressure.topicArticleId-277792,articleId-277694.html Wickwack 124.182.165.212 (talk) 03:53, 8 January 2013 (UTC)[reply]
I am not a registered editor and in conformance with Wikipedia policy I do not edit articles. If DRosenbach (the OP) is not happy with the wording in the article he cited, he is free to ammend it to make it clear only a partial effect is meant. Clearly all except Stu would be happy if DRosenbach does so. However, Stu just likes to argue, but apart from that he's pretty smart and at the end of the day I suspect he would support clarifying it too. Over to you, Mr Rosenbach. Wickwack 124.182.3.218 (talk) 14:06, 7 January 2013 (UTC)[reply]
I note that circle of Willis explains that the anatomy is variable, so I wonder if some people may be more resistant to the maneuver than others based on the capacity of their brain vasculature to reroute blood flow...
The idea of 'totally' depriving the brain of oxygen is physically absurd - degassing a solution requires considerable effort and is never truly absolute. The issue is only whether the oxygen level is sufficient. It would seem unnecessary to say "partially" deprive, but if the point is otherwise confusing to the readers, then that is what matters. Wnt (talk) 15:47, 7 January 2013 (UTC)[reply]
Clearly the phrase "immediately deprive the brain of oxygen" could be interpreted by one person (such as me the first time I read it) as "totally deprive" and by another person as "at least partially deprive". So why don't we just put in another wording that no one will misinterpret? I'm going to put in "immediately reduce the supply of oxygen to the brain".
(Spin-off question - separated from previous answers)
Over time atleast about 20 or so people have specifically requested that I register and take on the job of cleaning up certain Wikipedia articles that are in bad shape. Nearly as many have just requested that I register as an editor just to continue contributions to Ref Desk. Usually when this happens I provide an explanation on their talk page or on the Ref Desk talk page on why I'm not registered and why I do not edit articles. On occaison this has triggered spirited debate between various editors and admin folk, which is not a desired outcome. A search of archives will reveal that while you can edit articles without registering (which is one reason why I don't), most of the regular Wikipedia community do not like it, and it is against policy. A couple of years ago, after a spate of vandalism, unregistered editors were supposed to be prevented from editing articles, but never the less they still can, which I demostrated once by correcting a single word in one article. Incidentally, the reason why I do not edit articles is 1) because it is just too darn easy for work done with care to be undone by some peanut who hasn't done his homework, 2) certain admins have mistaken me for someone else and decided I should be blocked; 3) some articles are so bad it would take weeks of solid work to put them right. If anyone wants to know more about these articles or my reasons, invite me to your talk page. Wikipedia is an extremely valuable resource - it is a great pity that articles are subject to illinformed change and outright vandalism. Wickwack 121.221.229.133 (talk) 00:36, 8 January 2013 (UTC)[reply]
Sure, people will request that you create an account. I'll request it too! It's a good idea. But it's NOT a requirement...there are only around 4,000 articles (out of 4.1 million!) that you can't edit without an account. (See WP:SEMI for the rule and Special:ProtectedPages for a list of all protected pages). But you can edit 99.9% of articles without registering. Wikipedians tend to treat "IP editors" (those who edit without registering) with deep suspicion...that's unfortunate for you - but not without good reason. Almost all vandalism comes from IP editors and almost all IP editors (numerically) are vandals. So it becomes a knee-jerk reaction to suspect any IP editor of evil-doing. That's a bad reaction because there are without doubt a large number (albeit a small percentage) of excellent IP editors. But it is categorically not against policy to edit without registering. If it was, we could flip a switch in a configuration file and ban all editing by IP users in a heartbeat (I do that on all MediaWiki sites that I personally run). Your reasons for not editing articles are well-understood...but how can you demand that absolutely any idiot (specifically: any school kid with access to a school computer who should be doing a history class but is actually typing obscenities into the article about Barack Obama) be allowed to edit any article - and in the same breath demand that edits that you make should be sacrosanct and that nobody should ever change the golden words you've created? Don't you see that those are contradictory demands? Then you complain that people have "mistaken you for someone else" - well, duh! If your only identification is your computer's IP address and that address is given to you by your Internet Service Provider (using DHCP) - then the person with the address "121.221.229.133" is you today - and some horrible vandal tomorrow - and you again next week. It's inevitable that you'll be accused of all sorts of things that you didn't do. That's why creating an account here is a good idea. It's password protected, so the only person who can use it is you. Other editor's dealings with you will be consistent and your reputation will stand over long term. When people see User:SteveBaker - they see that I've been an editor for 7 years and made 25,000 edits and never once been blocked, banned or sanctioned. When they see User:121.221.229.133 - they know nothing about you and since people using that same "name" have been evildoers - it's just inevitable that you're going to occasionally be accused of doing evil. SteveBaker (talk) 14:42, 8 January 2013 (UTC)[reply]
I have made NO contradictory demands. You are confusing Wikipedia articles with Ref Desk. You are also confusing altering text in Wikipedia articles with posting new comments on Ref Desk, leaving other posts as they are. I have never altered the text posted by someone else. I monitored the Admin Noticeboard and talk page for a while - it is quite clear that there are good admins and bad admins, and quite clear that folk get blocked who darn well should get blocked, and folk who get blocked because admins take a sloppy approach or maybe just don't like something rattling their cage. I think allowing unregistered folk to edit Wikipedia articles is stupid. I think allowing people to post questions on Ref Desk without registering is ok - there's no conflict, they are two different environments with different purposes.
Yes, "deprive" can mean either "totally deprive" or "partially deprive". In the case of oxygen deprivation it obviously means "partially deprive", no matter what Wickwack claims, but clarifying the article is a good idea, to avoid confusing people like him. StuRat (talk) 21:01, 7 January 2013 (UTC)[reply]
Wickwack, can you point to this supposed "policy" about unregistered users not editing articles? As far as I know, there is no such policy. Unregistered editors are encouraged to register, but the system recognises that many people do not want to, for any number of reasons. You are still just as welcome to edit articles as I am, and you are subject to the same rules and standards of general conduct as everyone else. What registered editors may feel about your state of unregistration is none of your business, and you should not let it prevent you from editing articles. -- Jack of Oz[Talk]05:25, 8 January 2013 (UTC)[reply]
There is absolutely no policy forbidding IP's from editing articles; where Wick got this impression is well beyond me given A) how ubiquitous this type of editing is (I doubt more than one tenth of one percent of articles on the whole of the English Wikipedia has not had contributions from unregistered editors, most of them constructive and welcome) B) the massive amount of community discussion that went into forming the consensus that this was best all around for the project, a stance which has since remained the standard, with little serious challenge, since the earliest days of Wikipedia, and C)every major policy page concerning itself with the registration process and beginning editors makes it clear that, while there are significant advantages to registering (both for the editor and the project as whole), it is by no means required and anyone who can improve any article is encouraged to, even if they can't/won't register. I forget where in the Wikimedia framework reports on the exact figures are published (though I know the Signpost occasionally reports on them), but it seems almost a certainty that about half of all edits on this particular Wikipedia are made by unregistered users and mostly always been that way. Hopefully Wick can show us where he was misinformed on this matter, because if there's even so much as an essay suggesting a contrary consensus, it should be altered.
On a separate note, the degree of discussion above on a minor semantic point is asinine, bloated by petty conflict and not really doing much to assist the OP. For the record, my use of the word deprivation (and that of virtually everyone, I think) is without a doubt one that scales to context and does not necessarily mean absolute absence of the resource being withheld; I've never seen a formal definition in conflict with this in any dictionary, and I can't even begin to imagine how many times I've heard it used in my life, from countless individuals, in ways that are inconsistent with Wickwack's all-or-nothing interpretation. In it's common clinical uses, it's clear that it can refer to a partial absence.
Now, addressing the OP's question (and indeed the above absolutist debate on the definition of a single word is especially absurd given he refined the question for us further), yes, you are correct Rosenbach: "immediately deprives" is indeed an overstatement of the facts. As has been noted above, by Wick and others, a certain amount of oxygen will remain in the brain and, regardless of the hold, a certain amount will probably continue to flow into it; if the hold is successful in rendering the individual it is applied to unconscious, it is either the result of a certain threshold of oxygen supply not being met or, more likely, that the chemo- and baroreceptors involved have simply been manipulated to trigger this reaction. Indeed, the victim of the hold should hope for the latter since it doesn't take long for the brain to be deprived of oxygen (even in the sense of partial but significant deprivation) before there is significant risk of permanent injury. Snow (talk) 06:49, 8 January 2013 (UTC)[reply]
As for where I was supposedly "misinformed" - Ref Desk talk page. As I said above, if anybody wants to follow up what's wrong with certain articles, or my reasons for not registering or editing articles, they are welcome to invite me to a discussion on their talk page or admin talk page. This is not a discussion that should be here on Ref Desk. In fact this whole question, from the OP onward, should have been on the article talk page, not on Ref Desk. However, the OP did ask, he got the usual off the cuff unsupported crap from StuRat, which in this case was incorrect, and so I posted a correction and subsequent explanation in good faith. DuoDuoDuo corrected the article, so we have a good outcome. On this page, that should be the end of it - no further debate can be of any value to Ref Desk users at large. Wickwack 124.182.165.212 (talk) 07:16, 8 January 2013 (UTC)[reply]
I posted many references which prove that "deprived" can mean "partially deprived". It is you who made the absurd statement that it always means "totally deprived", with no references which back up that claim. StuRat (talk) 07:29, 8 January 2013 (UTC)[reply]
There's really no "supposed" about it - you were misinformed; Wikipedia policy not only allows for IP edits, it encourages them in cases where registration is not possible or undesirable to the editor (assuming it is not a case of sockpuppetry or other abuses). I'm not really interested in your motivation for not registering or not or editing or not as that's entirely your business and of no relevance here. But you're right as to the appropriate placement of this discussion in the first place; it probably would have been better served by taking place on the talk page from the start, though I understand the OP's motivation in coming here to establish a technical definition of the terminology involved. And yes, Stu sometimes bites off more than he can chew with highly speculative responses here, but in this case I happen to think he was entirely correct and helping the OP. I'm equally certain your initial comments were in good faith (though things would probably have been better off without that antagonistic jab at Stu in your very first response). However, you both clearly quickly let your stances and your responses become personal, resulting in the acrimony and bloat above. But let's allow it to rest here as it seems we've all come as close to consensus as we will on this topic and the OP is presumably satisfied. Though I'd like to make one quick side-note here and request that you not format other editor's posts on this page (at least not in-so-far as such tools as </small> tags go); it's inappropriate to make that decision for another editor. Snow (talk) 07:43, 8 January 2013 (UTC)[reply]
(Argh! This discussion really doesn't belong here - it's WAY off-topic - but corrections of fact need to be made).
Wickwack is somewhat correct - there are articles that (s)he cannot edit without registering an account and logging in to use it. Snow is also correct in that a guiding Wikipedia policy is that people should be able to edit articles without registering. The trouble is that widespread abuse of that policy means that we simply can't cope with every single part of Wikipedia being editable by IP editors. Hence, WP:SEMI says that some small number of "semi-protected" articles (those with a silver padlock in the top-right corner) can only be edited by registered users with at least four days service and ten prior edits.
So Wickwack truly cannot edit semi-protected articles such as Homosexuality, Computer or Wikipedia. That said, almost all semi-protected pages are templates, redirects or user pages. A few of them are articles that are being protected for the short term (days to weeks) against a short-term assault of IP vandalism (generally articles that are especially news-worthy and things that are currently on the front page). Generally, the only long-term semi-protected articles are about highly controversial or frequently-searched-by-annoying-schoolkids-from-school-computers topics (hence the three examples above). In one such article that I worked on for a while (Computer), we were getting vandalized to the tune of 40 edits per day by various "IP users" (people not using registered accounts) and over the course of an entire month that I searched, we didn't get one single good edit from an IP user. Over the same span, there was just one bad edit from a registered user and 30 or so good edits from registered users. The regular editors of that page became so overwhelmed by the effort in keeping the article readable that permanent semi-protection was deemed to be the only way to keep the article usable. Once in a while, some well-meaning admin will come along and remove the semi-protection from Computer and we're once again overwhelmed until we can persuade another admin to step in and turn it back on again.
This is unfortunate for people like Wickwack who edit in good faith from IP accounts - but in the face of such overwhelming abuse from IP editors - we really have no choice but to shut out the very, very few good guys in order to keep out the overwhelming amount of crap from the bad guys.
I don't understand why frequent good-faith editors who do good work and sign their posts with a 'handle' like Wickwack does wouldn't preserve their anonymity by creating an account (publishing your computer's IP address every time you post is very non-anonymous - I could almost certainly find Wickwack's real name and location from his/her IP address in under 20 minutes - but figuring out that information from a Wikipedia account name would be near impossible). But choosing not to create an account is something enshrined in Wikipedia principles that is unlikely to change. (IMHO, we should require registration for all article-space editing...but that's just me!).
As far as I know, none of the reference desks, or their talk pages are, or have ever been, semi-protected. It would be ridiculous if they were because almost all of our questions come from IP users. SteveBaker (talk) 14:05, 8 January 2013 (UTC)[reply]
This really doesn't belong here on this page, but why don't I register? Simple - as I said before, certain admins think I am someone else (which was very clear from their discusion on the admin talk page) and have invested a lot of time and effort to block me. If I registered, that would make it easy for them. As for privacy, you can use an IP locator - that will locate me to Australia immediately. Big deal, there's only 25 million of us. And each time I access the internet, I get a different IP anyway, allocated from a national pool. You will be able to discover the internet providor. Big deal, they only have about 4 million customers. If I registered, then admins do know who I am, and if it is hackable, so do villains. Having said that, I think allowing non-registered folk to edit Wikipedia articles is stupid. See post on your other comments above. Wickwack 58.169.236.195 (talk) 15:05, 8 January 2013 (UTC)[reply]
But if you used a registered account then nobody could mistake you for anyone else and this mess would never have happened. In fact, if you registered now (preferably with a handle other than Wickwack), nobody would be aware of any of this past confusion and you'd be able to edit as you with whatever respect you deserve from the quality of your posts. As for locating you, unless your computer has the security of Fort Knox, anyone with the right set of black-hat hacking tools will be able to reach the computer that you're using right now via it's IP address, prod it until they gain entry to it and from there all bets are off. If you use a registered account then the only way to connect you to a specific computer is via the "checkuser" extension which is only used rarely, by a few individuals (just 43 of them at last count) - and after considerable oversight. There are very few places where your IP address is made public like it is if you edit Wikipedia without an account...there is a good reason for that! SteveBaker (talk) 17:17, 8 January 2013 (UTC)[reply]
Maybe. My experience is that there was someone that the admins didn't like. He tended to post a lot of comments of Ref Desk, but not anything that would justify blocking. He also participated in article talk page discussions - which I've never done. Judging from the admin page discussion, they think that each time they blocked, he re-registered with different data to get around it. Then when I popped up and posted on Ref Desk they blocked me. Sometimes they block an IP address, cutting me off - that's completely stupid, as the IP address changes from one session to the next. It might be in this case sometimes it wasn't me they were aiming at - that's what they said when I complained once. Wickwack 124.178.62.219 (talk) 02:05, 9 January 2013 (UTC)[reply]
Again, your defense in the event that you happen to get handed the same DHCP IP address as some blocked Wikipedia vandal is to simply register an account. Problem 100% solved! SteveBaker (talk) 04:06, 9 January 2013 (UTC)[reply]
If the IP address is blocked, it's blocked, whether the temporary user of that address is registered or not. Either way, shut down one's internet session and start another - problem solved. My point was - admins sometimes do dumb things. And if they block a registered user, he can't use his registered identity regardless of his current IP address - but he can just go ahead and continue, either by re-registering or operating as an unregistered user. So if one can't post on Ref Desk, one doesn't really care why, just restart unregistered and it will work. Can you not see that? Wickwack 121.215.21.138 (talk) 04:35, 9 January 2013 (UTC)[reply]
Blocking an IP does not necessarily block registered users who happen to have that IP. Blocking an account sometimes also automatically block various IPs that that account uses. But the ref-desk is decidedly not the place to continue this discussion. The technical aspects are well-documented, and the philosophical and pro/con debate wore out its welcome years ago. DMacks (talk) 04:50, 9 January 2013 (UTC)[reply]
I would also point out the actual admin involvement (as admin) here in recent times has been limited anyway. A lot of the accounts and IPs blocked in recent times have been at the request of someone like me, a non admin. So blaming it solely on admins is somewhat missing the point. Right now there is a persistent sockpuppet who is back after being blocked about 1-2 weeks ago again after making disgusting claims about someone (after they were allowed on the RD for several months). In fact there is another editor who also appears to be a reincarnation of a minor sockpuppet who got banned for amongst other things continuing to ask the same offtopic and unanswerable questions (ironically also from Australia but generally using Optus and not from WA). Incidentally I'm unconvinced of the claim that Telstra only has a national IP pool. Whenever I geolocate Wickwack (and I did it again with the above IPs as well as one from May last year just to check), I always get Western Australia (actually Perth but that's probably false precision) which seems to correlate with information WickWack has mentioned before. I'm not saying Telstra geolocation is always entirely accurate but I do know there are plenty of Telstra ranges which do not geolocate to Perth (and again I seem to recall one or two instances where the geolocation tallies with the information revealed by the person behind the IP). This suggests to me the geolocation isn't entirely inaccurate and Telstra do actually have distinct pools based on some degree of geographical area (obviously the pools aren't constant although with IPv4 exhaustion perhaps they will start to be....) Nil Einne (talk) 01:16, 10 January 2013 (UTC)[reply]
I'm not going to claim my computer is a Fort Knox in terms of security, though I do use security software and a hardware firewall both from reputable manufacturers, and I didn't leave the settings at the default loose level of protection. Where there is a will, there is usually a way, so a clever enough villain could get in. Attempts have been detected and dealt with. The thing is though, such villains don't need the IP addresses displayed on Ref Desk, which mostly are only allocated to a user for one session anyway. They can just probe thru the range of IP adresses and the ports at each address. My security software shows such probing attempts nearly every time I display its' reports, and this is how it has been since well before I started posting on Ref Desk about a year ago. Wickwack 120.145.59.25 (talk) 12:27, 10 January 2013 (UTC)[reply]
I am slightly disappointed, and surprised, to hear that IP editors are treated with 'deep suspicion'. Until registering about 14 months ago I was a long-term IP editor (about 26 months, just over 11,900 edits). My experience as an IP was 99.9% positive in interacting with other editors. Very rarely did I get 'nasty' messages. (The only one I remember was from another IP editor!) What really makes me suspicious is a new account with a name like "Suckmypen15123" or "Phuckinstick", both are real accounts!
I suppose I was fortunate to have a static IP for that entire period, also my first edit was undoing some vandalism (and I used an edit summary too!) I see what new editors (IP or not) get up to, and spend time reverting (and helping) them, when necessary. But they also do a lot of good edits. I think often they are newbies making their first edits and simply not sure what is the right thing to do, hence often in good faith putting un-sourced (but correct) information onto pages (As I see I did too, 40 months ago). I recently reverted an un-sourced IP edit to a towns population figure, which I soon found was exactly correct. I just had to source it correctly, The IP tried, but obviously didn't know the exact way to do it. - 220ofBorg17:33, 9 January 2013 (UTC)[reply]
Bug identification
Can someone please identify this bug for me? WARNING: GROSS, click at your own risk:[3]. I'm in the Laurentian Great Lakes region. I found the bug indoors. Dncsky (talk) 09:03, 7 January 2013 (UTC)[reply]
I bought a replacement synchronous motor for a microwave oven. The label shows TYJ50, AC 220-240V, 50/60Hz, <4W, 33r/min but no manufacturer. It is cylindrical, of diameter about 50mm and length about 15mm, and was a cheap online purchase. Before going to the trouble of installing it I tested it and though it runs at near enough the rated speed, the case gets too hot to touch after 5 minutes unloaded. Is that to be expected with this kind of motor? — Preceding unsigned comment added by Semiable (talk • contribs) 14:35, 7 January 2013 (UTC)[reply]
It seems unlikely that the motor is expected to get that hot in service - but perhaps it's supposed to be bolted to the metal frame of the oven - and that conducts the heat away and radiates it over a larger area to act as a heat sink. It's hard to tell. SteveBaker (talk) 20:31, 7 January 2013 (UTC)[reply]
Are there any creatures in existance that sport an odd (even just one) set of appendages? Suppose a "half" creature with just one brain lobe, one eye, one leg, etc. Or say a tri-lateral layout. Have any of these been observed, especially in the case of a single-sided organism?
75.220.96.17 (talk) 15:02, 7 January 2013 (UTC)[reply]
Starfish have five-fold radial symmetry. They really don't have a single brain, but instead a ring of neural material that goes around the central hub. A starfish can be cut up (with a cut taking a whole limb and the associated central segment) and that single limb is a viable independent creature which will eventually regenerate back into a 5-fold starfish again.[5] -- Finlay McWalterჷTalk15:07, 7 January 2013 (UTC)[reply]
Adult flatfish are one-sided (example), having two eyes on either the left or the right side of their body. However they acquire this asymmetry during their youth, as they are hatched symmetrically. There are also the extinct Trilobozoa with tri-radial symmetry. - Lindert (talk) 15:17, 7 January 2013 (UTC)[reply]
Male Fiddler crabs are asymmetric. (A wierd thing about these crabs is that if they should happen to lose their giant claw, the claw on the opposite side will rapidly grow to enormous size to compensate - and the missing claw will regenerate as a tiny claw.) But I suspect that symmetry is so common because it results in a huge saving in the amount of DNA an animal needs. SteveBaker (talk) 15:33, 7 January 2013 (UTC)[reply]
The majority of animals are bilateria, including even starfish (which basically start to bend right when they become teenagers, until they they have bend once around and lost the left half of their body). Some animals loose some of the symmetry during later developments. Animals which have no symmetry are e.g. sponges. And WHAAE, in this case Symmetry in biology. --Stephan Schulz (talk) 15:45, 7 January 2013 (UTC)[reply]
Of course, despite being called bilateral symmetric, (and this is sorely ignored in our article), no mammal is actually symmetric, and in fact imposing left-right asymmetry through Nodal is crucial in early embryogenesis. Fgf10 (talk) 19:28, 7 January 2013 (UTC)[reply]
Indeed. See also situs inversus, etc. Thinking about it, I would suppose one could almost come up with a sort of biological theorem here, though - we tend to think of animals as bilaterally symmetrical because they start off with a mirror plane and then adjust development afterward. The ultimate reason is that in order to have a plan of development, you have to define one axis (radial symmetry), then another - bilateral symmetry - but only with three separate axes defined do you break from that plan. So in order for an animal not to be bilateral symmetric at the beginning it would need to define all three axes, and do so immediately, and what is the selective pressure for that? Either that or, like sponges and plants, just not have much of a plan. Wnt (talk) 21:42, 7 January 2013 (UTC)[reply]
Very good point, and I can't imagine a workable system where asymmetry isn't generated through a 'disruption' of initial symmetry. You'd have to have very well specified polarised cell divisions from division 1 onwards, I guess. Fgf10 (talk) 22:07, 7 January 2013 (UTC)[reply]
Nobody is arguing that there isn't asymmetry in detail (your heart, liver, pancreas are all highly asymmetric). But please re-read the OP's question. We're being asked about animals with gross asymmetry - like having one arm on one side of the body and two on the other (like the fictional "Moties" in The Mote in God's Eye). I'm having a hard time coming up with real-world creatures like that (although the fiddler crab and adult flatfish are close). Nature loves symmetry - because it's efficient...but it's not perfect symmetry. Humans have two, symmetrically-placed, kidneys - which is great - if you lose one, you can still live out a fairly normal life with the other. However, we have only one (highly asymmetric) heart and one liver - and if you lose either, it's curtains for you. When you only have one of some organ, placing it symmetrically is difficult - there just isn't room on the center-line of the body to place everything in the middle.
Evolution is all about optimizing efficiency. Having most things be symmetrical saves on genetic information to code the two halves of our bodies separately. But slavish attention to symmetry is inefficient in other ways - hence only having one liver and one pancreas and putting them on opposite sides of the abdomen is more efficient than having just one of each on the centerline or duplicating functions by having two of each, symmetrically placed like the kidneys.
Left/Right-handedness is a similar deal. We have a symmetrical brain - but there isn't enough computing capacity in it to duplicate functions and have things like manual dexterity or eye dominance in both halves - so we break symmetry to save space - and as a result, we have one hand that's more useful than the other and mathematical functions present in just one side of our heads.
Evolution probably took some complicated path to get to this situation - yet it's still a little surprising that strongly asymmetric exterior forms are so incredibly rare in nature.
Very good points. Yes, gross symmetry is efficient, but generating asymmetric localisation does not require extensive genetic differences in both halves, so is not a big efficiency loss. Asymmetric expression of certain key signalling molecules, Nodal and Lefty (yes, the gene is actually called lefty) is enough to promote asymmetry. I'd be surprised if this isn't the mechanism that forms the one large claw of a Fiddler crab, but I couldn't find the exact mechanism in a quick search. I couldn't see making even something like Moties as being impossible in this way. Maybe in the case of a Fiddler crab having one big claw is sufficient, so it's actually more efficient to develop it asymmetrically and not waste energy on growing a second? Fgf10 (talk) 15:54, 8 January 2013 (UTC)[reply]
As I pointed out before, the weird thing about the fiddler crab is what happens if the large claw gets amputated. In this case, the OTHER claw grows huge and the missing claw regenerates with a small pincer...what you end up with is a mirror-image of the original crab. It's tough to explain this with the Lefty gene. SteveBaker (talk) 16:53, 8 January 2013 (UTC)[reply]
Sounds like a standard case of positive feedback: a big claw keeps the other claw small, a small or missing claw makes the other claw big. Genetics tend to act more like a recipe than a blueprint; a single change often has multiple effects. --Guy Macon (talk) 19:15, 8 January 2013 (UTC)[reply]
Just nitpicking: The human kidneys aren't symmetrically placed: The right kidney is placed a bit lower than the left kidney.
The narwhale is an example of asymmetry trying to pass for symmetry. The "horn" is normally the left tusk, but is close enough to the center that it's not obviously asymmetrical, unless you look closely. StuRat (talk) 20:48, 8 January 2013 (UTC)[reply]
Is it true that the more human hair is smooth\straight, the more it is likely to dropout?
In other words, can we generalize that populations that generally have UNsmooth hair, Like Non-asian Males in general, some African peoples, Yemeni Arabs, and Australian !!! Aboriginals, will tend to have LESS natural hair dropping?
what are the proteins \ chemicals that exists in straight hair, that contribute much to the odd of it's dropping?
I'm wondering if you might need to narrow down "Aboriginals" a bit. We all have ancestors who were "aboriginal" to somewhere once. I will agree, based on purely original research among lots of examples of friends my age (60+), that baldness is (almost?) non-existent among Australian Aboriginal men. I'm quite jealous. HiLo48 (talk) 22:19, 7 January 2013 (UTC)[reply]
Note that Baldness and hair dropping are not the same.
I remember reading decades ago that the fairer one's hair, the thinner the hair, and the more likely baldness is, with the exception of red hair, which is the thickest and whose bearers are least likely to go bald. From what I remember I wouldn't call the book a reliable source, though, and a quick google search only gave info on either hairloss and hair dyes or what color bald men have on their driver's licenses. μηδείς (talk) 02:59, 8 January 2013 (UTC)[reply]
Quantum fuse
There's a fallacy in quantum physics that I've been thinking of, but I
haven't found the proper name for it yet. As a placeholder I'm calling
it the quantum fuse, because it acts like a fuse you light for say a
bomb.
Take a very pure block of some semiconductor, silicon will do, and
carefully dope it so it has a long line of holes in it, each of which
can comfortably hold one electron. Above all but the last hole is an
electronic circuit that will insert one electron into each of these
hole, all at exactly the same time. I.e. the first through the next to
last hole will be filled faster than a vacuum photon could cross that
distance. At the first hole there is an additional electron ejector
that can be set to fire at the exact same moment as all the rest. And
at the last hole there is a sensor that will read out if it has been
filled or not.
For a logical zero the additional ejector does not fire in that extra
electron, and so every hole except the last one will be filled at the
same moment and the last hole will read zero.
For a logical one the additional ejector does fire. The first hole
gets two electrons, but can only hold one so one of these tunnels over
to the second hole. Since any tunneling event is instantaneous, the
excess electron arrives in the second hole at the same moment an
electron is added to fill that hole. And so one of the electrons is
bumped over to the third hole and so on. Ergo the final hole in the
series gets filled before any signal could have arrived from the
additional ejector.
Your fallacy is that you depend on a fictional, hypothetical "electron injector" whose mechanism (which you did not explain) is inconsistent with any actual device you could actually build. Your entire thought-experiment depends on the guarantee that your electron-injector will put an electron into the circuit. Yet, you did not explain how and so you didn't consider the scenario that the injected electron doesn't go where you want it to. Diffusion of electrons depends on the state of the semiconductor; adding electrons will saturate the charge carriers. This reduces the current; or, quantum-mechanically, reduces the probability that an individual charge-carrier will actually move. But, this need not even be treated quantum-mechanically: we use the saturation model to estimate properties of devices without ever considering quantum effects. If you want to solve analytically at the atomic level, you will get even more accurate results because you'll derive diffusion coefficients for every single constituent charge-carrier. Nimur (talk) 16:29, 7 January 2013 (UTC)[reply]
Tunneling isn't instantaneous. It can appear to be faster than light, even in classical electrodynamics (where you can get tunneling of light between fiber-optic cables, for example), but what you're actually seeing is (I think) a quadratically extrapolated signal, analogous to the familiar fact that the electric field of a moving particle appears to come from a quadratically extrapolated "current location". Also, the exclusion principle isn't absolute—it's just the lowest-energy states that are filled, and there is always room for more electrons if you supply enough energy. So I think your fuse, if it works, will work by means of an ordinary pressure wave, like Newton's cradle. -- BenRG (talk) 17:06, 7 January 2013 (UTC)[reply]
This is an intriguing question - I haven't answered it myself, but I can point out a few things. First, we have articles quantum tunneling, faster-than-light, and Raymond Chiao which express the root observation that tunneling is "1.5 to 1.7 times" faster than light. But the Chiao article expresses some doubt about it, and I haven't determined the current thinking on the point. I think that if it is true then there should be many other ways to get to the same end of making the effect macroscopic - for example, I think you might have what begins as a single photon pass through a long series of tunneling barriers, while being in a lasing medium to increase its intensity (to make up for reflection losses in tunneling). Wnt (talk) 18:21, 7 January 2013 (UTC)[reply]
Quantum tunneling is the same as tunneling in classical relativistic wave theory. The "tunneling" case is the case better known as "total internal reflection", where Snell's law implies that the wave number perpendicular to an interface must be imaginary on one side. This leads to exponential decay instead of oscillation in the perpendicular direction (e-kx instead of eikx), while the wave still oscillates in the parallel direction and in time (as required by the boundary conditions). This looks like the lower image on the right, where the medium on the left has a higher refractive index (the image is missing the internally reflected wave, though). If you put another medium of higher refractive index on the right, some of the wave will leak into it as an ordinary propagating wave (attenuated by an amount exponential in the width of the center region). The fact that the wave crests are horizontal instead of diagonal in the center region is what leads to the notion of "instantaneous propagation": it looks as though the phase of the wave simply skips over the central region regardless of its width. However it's a theorem of classical relativistic wave theory that you can't send a signal faster than light. In the quantum case everything is exactly the same mathematically, and so the natural conclusion is the same, but people tend to get all woo-woo as soon as you attach the name "quantum" to something.
A similar argument was once invoked to prove that the speed of gravity must be much larger than c: if the Sun's influence on the Earth lagged by 8 minutes, the Earth would be pulled toward the location of the Sun 8 minutes earlier, which would add a backward drag component to the total force, which would have long since led to the Earth spiraling into the Sun. But it doesn't work that way in relativistic field theory: although the force depends only on the Sun's position 8 minutes earlier, it is actually directed toward an "extrapolated current location" of the Sun. Likewise, a tunneling wave emerges with an "extrapolated future" shape. As long as the tunneling time is small compared to the effective time resolution of the wave, the extrapolated wave will be indistinguishable from the real thing.
I've always experienced basements to remain at a comfortable temperature, but now I live in a house where it's nearly as hot/cold as outdoors. Why?
All my life I've loved the basement - it's the coolest place to be in the summer and in the winter it's comfortable as well. A few months ago I moved in to a house that has a basement that seems to perpetually be just a little bit warmer than the outside temperature - in summer it's miserable, and in the winter I can almost see my breath (I live in Minnesota). How is this one different from literally every other basement I've been in for my entire life? I thought it was just as simple as being below ground. NIRVANA2764 (talk) 16:23, 7 January 2013 (UTC)[reply]
I suppose we could look up heat conductivity of various kinds of soil, but first, can you assure us that the basement is actually well enclosed from the outside air? (For example, you could look at the circulation of smoke) Wnt (talk) 18:01, 7 January 2013 (UTC)[reply]
Agreed. It's probably drafty windows. Another factor is how much heating or A/C your basement gets. Some forced air systems leak air all over the place, down there, while others are pretty tight. StuRat (talk) 20:46, 7 January 2013 (UTC)[reply]
Does paper really dull scissors faster than cloth does?
For many years I have noted with amusement the following quirk of human nature:
Many engineers and technicians who do fine work with paper swear that cutting cloth will ruin their scissors. I saw one worker who trimmed filter paper for an aerospace application putting a padlock though the scissor handles when not in use.
Meanwhile, many people who do sewing swear that cutting paper will ruin their scissors. I have seen claims from both groups that one snip of the wrong material means you have to buy new scissors. I wouldn't be surprised if MDs made the same claim about surgical scissors.
I searched for anyone who had done actual testing. Didn't find anything but I did find this. I am thinking of emailing them if nobody here has an answer.
It's kinda-sorta possible for both statements to be true. I doubt they are - but let's play devil's advocate for a moment. Scissors are held together with a screw or rivet - when the scissors are badly worn, this opens up, gets loose and makes a bit of a gap between the blades - which makes them cut less effectively. Suppose (for the sake of argument) that cloth is thicker than paper and cutting it tends to bend/wear the rivet more quickly than paper...and let's suppose that phytolith (or whatever) in paper physically dulls the blades by wearing them out in ways that cutting cloth does not. It's then possible that cutting cloth with scissors that are only used for paper would bend open the rivet and make them less effective - and also that cutting paper with scissors that are only used for cloth would dull the blades and make them less effective too. If scissors cut well providing they EITHER have a tight rivet OR sharp blades - but fail to cut will if they are both dull and loose - then the result would be that mixing the two materials would indeed prematurely wear out the scissors.
Now - to be 100% clear - I'm not seriously suggesting that this is literally the case - merely that it's not impossible for two different materials to wear out the same pair of scissors in two different ways and thereby render this seeming paradox correct.
In all likelyhood, it's all an old-wives tale and it doesn't matter a damn which scissors get used for what. My impression is that most people who do sewing keep a "good" pair of scissors for their work and simply don't want them to go missing as other members of the household take them for other purposes. The story of the aerospace guy with the padlocked scissors is almost certainly that. I mean - just how often would someone in a aerospace engineering workplace take them to cut fabric?!? It's much more likely that they'd often be "borrowed" and simply not returned. Hence the likely myth of incompatibility would serve the scissor owner's needs and would rapidly become lore and passed on to future generations...true or not.
Well, if it's filter paper, the person using whatever has been filtered might be touchy about pieces of thread, paper, and tape turning up in his liquid. Wnt (talk) 21:08, 7 January 2013 (UTC)[reply]
Along the same lines, there really can't possibly be a reasonable answer to this, if only because the umbrella terms "paper" and "cloth" can refer to any number of materials with varying physical properties likely to wear or provide stress on the scissors in different ways (to say nothing of the variables involved in the composition and form of the scissors, the cutting technique involved, maintenance of the blades, whether they are used continuously or intermittently, and just a whole huge mass of other factors). Certainly it's clear that, especially in an industrial context, many different types of scissors have been developed for specific tasks and materials. Snow (talk) 07:54, 8 January 2013 (UTC)[reply]
Yes, so again, there isn't necessarily a paradox in the idea that scissors that are designed for cutting cloth might be ruined by cutting paper - and vice-versa. However, I still very much doubt that people who cut cloth using $10 scissors bought from the needlework department at WalMart would be able to detect any significant blunting from using them to cut paper occasionally. All I'm trying to point out to our OP is that the seeming paradox of opposing views on scissor blunting doesn't (by itself) disprove either of the opposing theories that the various sides of the debate are proclaiming. Someone needs to do some experiments. Take two identical pairs of scissors - measure their initial cloth-cutting capabilities - then use one to cut 100 meters of cloth and another to cut 100 meters of paper - then re-measure their cloth-cutting abilities. If there is a strong difference - then maybe there is something behind this. Then you need to re-do the experiment, reversing the role of paper and cloth. Obviously you'd need to repeat the experiment a few hundred times to be sure that the results were statistically valid. Since this is a whole lot of work - it's easy to see why we don't know the answer! SteveBaker (talk) 14:56, 8 January 2013 (UTC)[reply]
I can't speak for the relative wear rates of paper and cloth, but I have a pair bought 37 years ago on a market stall and used for everything needing cutting, and they work as well now as when new. The key might be a domed spring washer keeping the blades together. Semiable (talk) 20:46, 8 January 2013 (UTC)[reply]
I also have a pair of fairly ancient scissors that were probably made in the 1950's for cutting wallpaper. They are occasionally useful because they have unusually long blades and don't suffer from left-hander-hostility like so many modern scissors! They also cut well - and (as User:Semiable says), the important part is the part that keeps the blades together. I have no idea what they were originally fitted with - my father had them held together with a wing-nut and bolt with a spring washer. I find myself replacing that nut and bolt every few years when they wear out and start to need to be re-tightened annoyingly often. I've occasionally sharpened them with a Honing steel - but for me, the sharpness of the blades is a small matter compared to getting the tension right between them. SteveBaker (talk) 21:29, 8 January 2013 (UTC)[reply]
If you read the section of the article you just linked to which mentions 'sawback' bayonets, you will find a fairly comprehensive answer. But in summary: they are more damaging, but not necessarily more readily lethal, and they have a tendency to get stuck in the wound, rendering the attached rifle useless and the attached soldier a sitting duck. They are also viewed as needlessly cruel: if you're going to stab someone on the battlefield, doing so in a way that does not deliberately torture them if you fail to kill them outright is considered a good idea. AlexTiefling (talk) 19:05, 7 January 2013 (UTC)[reply]
I read this after watching an episode of Futurama, and got a silly mental image of Fry (though Zapp would make more sense) swiveling a rifle with a dead soldier flopping on its tip. —Tamfang (talk) 15:44, 1 July 2013 (UTC)[reply]
I think they were only used by the German Austrian armies, where they were issued to pioneers and called a pionier-faschinenmesser ("pioneer fascine knife").[6] A fascine was a large bundle of sticks used in field fortification or trench-crossing. Otherwise, I agree with Alex's comments above. Alansplodge (talk) 19:41, 7 January 2013 (UTC)[reply]
"During the day we loaf about and make war on the rats. Ammunition and hand-grenades become more plentiful. We overhaul the bayonets--that is to say, the ones that have a saw on the blunt edge. If the fellows over there catch a man with one of those he's killed at sight. In the next sector some of our men were found whose noses were cut off and their eyes poked out with their own saw-bayonets. Their mouths and noses were stuffed with sawdust so that they suffocated.
Some of the recruits have bayonets of this sort; we take them away and give them the ordinary kind.
But the bayonet has practically lost its importance. It is usually the fashion now to charge with bombs and spades only. The sharpened spade is a more handy and many-sided weapon; not only can it be used for jabbing a man under the chin, but it is much better for striking with because of its greater weight; and if one hits between the neck and shoulder it easily cleaves as far down as the chest. The bayonet frequently jams on the thrust and then a man has to kick hard on the other fellow's belly to pull it out again; and in the interval he may easily get one himself. And what's more the blade often gets broken off."
I should add that apparently there's some confusion on the web about this point, with people talking about it being variously improper to use notched, sharpened, dull, or rusty bayonets - one source ties it to the 1899 Hague convention against "To employ arms, projectiles, or material of a nature to cause superfluous injury;". If you ask the Humanities desk I bet you'll get a better answer. Wnt (talk) 20:44, 7 January 2013 (UTC)[reply]
Thanks for that quote Wnt. That explains why they weren't used after WWI; I haven't got a reference for that, but a thorough Google only revealed 19th and early twentieth century examples. Alansplodge (talk) 22:33, 7 January 2013 (UTC)[reply]
There was a question about serration on swords on the Ask a historian subboard of reddit just yesterday, and it included a fairly long discussion on serrated bayonets as well. Consider looking there as well, if it's not precisely that discussion that started you on this tangent. 164.71.1.222 (talk) 06:00, 8 January 2013 (UTC)[reply]
Worth mentioning is that bayonets are almost never used for stabbing enemy soldiers. Some years ago, I came across a list dating from the American Civil War of things a bayonet was useful for (candle holder, utility knife, cooking spit, etc.), and most of them work better with a non-serrated bayonet. --Carnildo (talk) 03:47, 9 January 2013 (UTC)[reply]
January 8
How strong magnetic field at a distance from a magnetic source?
This is not enough information to solve for the field strength at one meter distance. If you provided information about the source, we could estimate the strength at other points. For example, our article on dipoles provides a simple formula for calculating the magnitude of a dipole source. Many magnetic field sources are well-approximated as dipole sources. Nimur (talk) 01:19, 8 January 2013 (UTC)[reply]
Er... magnetic monopoles have not been proven not to exist, they are perfectly valid in hypothetical scenarios, and at any rate that is the essence of Nimur's comment... 72.128.82.131 (talk) 02:21, 8 January 2013 (UTC)[reply]
The source is a speaker sub 8" with other magnetic sensitive equipment at 0.2 - 0.3 meters distance. The media is ordinary air. The only obstacle may be tree panel ~2cm thick. Electron9 (talk) 08:48, 8 January 2013 (UTC)[reply]
You still have not provided sufficient information. Firstly, there are two main types of speaker magnetic circuit construction: 1) cylindrical magnet in centre and soft iron flux return circuit outside; 2) Soft iron pole piece centre and magnet in the form of a toroid on the outside. Type (2) is normally used if the magnet is a ferrite magnet. Because the flux density of ferrite magnets is less than for metal types, ferrite magnets are usually oversized so that the pole piece is saturated or close to saturation. This means a lot more flux "escapes" with type (2) magnet systems. Also, the amount of flux at the distance range you indicated will depend on the diameter of the magnet system - this can vary 2:1 or more for the same size speaker overall diameter. The amount of flux that "escapes" also depends on the voice coil gap - the wider the gap the more flux escapes. Hi fi speakers are often made with ferrofluid lubricant in the voice coil gap - this will reduce the amount of escaping flux. The construction and material used for the speaker frame/basket will also have an influence. Be aware that speakers are available in low field models - these have a surrounding magnetic shunt to contain flux that would otherwise escape. These speakers were developed for use in TV sets with cathode ray tube (CRT) displays - such displays are rather sensitive to magnetic fields, especially colour displays. A high efficiency high quality speaker made for car radio applications can have an external magnetic field very considerably stronger than that of a speaker made for a cheap TV set.
All this means that, unless you have access to comprehensive magnetic circuit data from the manufacturer, the amount of external flux will be impossible to estimate and you'd be better off to obtain a candidate speaker and test it. If you have no means of testing, use a compass. Position the speaker so that it's field is at right angles to the Earth's magnetic field at your location, as shown by the compass. Move the speaker towards the compass so that the compass needle deflects. You can then calculate approximately the field strength of the speaker flux as a fraction of the local Earth magnetic field strength from the angle of deflection. For instance, a 45 degree deflection would indicate identical strengths.
How sensitive is your sensitive equipment anyway? I have some quite standard 8 inch speakers that produce no deflection of a compass at a separation of 200 mm. Keit 58.170.141.154 (talk) 10:28, 8 January 2013 (UTC)[reply]
As data on the speaker is missing. Perhaps one can figure out how many times less the field is at a distance than at the magnetic source ? A compass also has some inertia (but I like the idea). Electron9 (talk) 13:14, 8 January 2013 (UTC)[reply]
No. You could, if the point of interest was remote from the magnet, determine the fall off at another point even further away, as you could then assume a far field from a simple round rod magnet (the proverbial spherical cow approach). But you said you are interested in a point as close as 200 mm from an 8 inch (200 mm) speaker. Even if you assume the frame to be non-magnetic, if the speaker has a type 2 magnetic circuit (as I described above), the diameter of the magnet toriod will be around 50 to 80 mm. This puts you in the near field, so a far field approximation cannot be used. And you would still have to make a field strength measurement anyway for the reasons I gave - you haven't identified the magnet structure (type 1 or 2 or some other), you haven't identified the magnet diameter, presence or not of magnetic shielding/shunting etc etc. You gave the magnet strength (2.4 Tesla) but if this is speaker manufacturer's data it will be the total flux in the voice coil gap. Almost all of this flux is contained within the soft iron return circuit and shield (if fitted for TV use). You don't know how much of it escapes outside the speaker structure, but it will be a very small portion.
To see what I am talking about using the terms "far field" and "near field" consider a rod magnet of some arbitary area x mm2 having a total internal flux y. Close up at the poles, the flux density will be y/x. Close to the sides it will be less. At a point z metres far from it the flux density will be then (y/x).k where k is a reduction constant depending on distance and bearing relative to the magnetization axis. There is a standard formula for calculating k - Nimur gave you the link - but that need not concern us now. Now, take a second magnet made of the same material, but twice the area. Clearly, close up the flux density will be y/x i.e., same as for the first magnet. But at the far point the flux density will be 2(y/x).k, twice as strong as with the first magnet.
The inertia of the compass needle is of no importance whatseover, as you only need a stable deflection off normal.
Thirty seven...I think...the history of these things is complicated, confusing and very ugly! According to the last two sentences of our IC4 article: "In November 2011 two IC4 trains each failed to stop at stop signals. This caused the authorities to ban the IC4 from running until the problems had been investigated. The investigations are currently ongoing." ...and... "On 2 July 2012, the DSB announced that Trafikstyrelsen (Transportation Authority) has approved the Danish railways to be able to put into service the park 37 IC4 who had been withdrawn from service in November 2011."
So if they'd all been withdrawn from service in 2011 - and 37 put back into service last July - then there are (presumably) 37 in service today....although I suppose it's possible that more have entered service in the past 6 months...or that although DSB was approved to put 37 back into service, they might not have done that for whatever reason. Those possibilities aren't mentioned in our article or the sources it references - so the best answer I can find is "thirty seven". SteveBaker (talk) 13:22, 8 January 2013 (UTC)[reply]
Well, the answer is a bit complicated. Let's shoot for something simple and let the guru's here complicate the answer to the point that neither of us will be able to understand it!
Electrons are often thought of as tiny little balls that go around the nucleus of an atom like planets around a star - that's a nice mental image - but it's not really true. The "truth" is a bit different from that. At the level of atoms, the world isn't like the familiar world of human-scaled things. Particles are waves and waves are particles - mass and energy are the same thing. That's true at the scale of humans too - but it's very hard to tell. But at the scale of an electron, those weird things come to dominate any explanation. Nothing has a definite location. So an electron is more like a fuzzy cloud of "probability" - that's to say that the exact location of the particle isn't a definite thing - all we can ever know is that it has some probability of being at some point - and that probability is higher here than it is there. When you consider that, the questions you pose stop making any real sense.
Adapting my answer from this old thread: electrons do fall into the nucleus. The electron of a hydrogen atom doesn't orbit the proton, it's simply superimposed on it. They don't collapse to a point because the uncertainty principle forbids it. A decrease in position uncertainty beyond a certain point implies an increase in momentum uncertainty which leads to an increase in position uncertainty. Instead they settle into an equilibrium state where these two effects balance out. The electron ends up with a much larger uncertainty of position because its much smaller mass means that a small uncertainty of momentum counts for much more in terms of velocity. That's why the atom looks like a small nucleus of positive charge surrounded by a big cloud of negative charge.
When there are more electrons, the exclusion principle means that they can't all sit in the same place as the first one, so they end up in higher-energy states. Some of these are just more energetic versions of being superimposed on the proton (2s, 3s, etc.) while others (p, d, f, etc.) have angular momentum, making them more like orbits. The motion (if you can call it that) is nonetheless quite chaotic because of the uncertainty principle; the electron ends up spread out over the entire orbit. But electrons far from the nucleus in a Rydberg atom can have orbits that look almost like planetary orbits for a short time. Electron orbitals and planetary orbits are two extremes of the same thing. -- BenRG (talk) 17:42, 8 January 2013 (UTC)[reply]
Related question: From the formula of the 1s orbital, it looks that the electron is more likely to be within the nucleus than in any other shell of equal volume (i.e. with positive inner radius). Is that right?
Not sure about it, but I came to the same conclusion. The notion that the electron is never at r = 0 comes from the fact that the probability to be at any given point is zero. However, being within the nucleus doesn't imply that, it implies that r is very small but can be nonzero. Thus, electrons can enter and exit the nucleus without interacting.
That Heisenberg line is brilliant (but quite unrelated to the question). I only knew Schroedinger: "My cat ate my homework, and now the poor thing looks like half-dead." - ¡Ouch! (hurt me / more pain) 07:32, 10 January 2013 (UTC)[reply]
Sub Questions
It is clear that electrons do not move in orbits, but still I have some confusions. Do electrons move around nucleus or they remain at the same site ? If a electron is not at rest, the orbital in which it lie should also move with this electron. Does this happen ? Can a electron change its orbital ? Parimal Kumar Singh (talk) 13:26, 9 January 2013 (UTC)[reply]
As I understand it, dozens of illustrations have taught us that electrons are little black spheres, and neutrons and protons are not so small spheres, red and white in color. We need to lose that image when thinking about "real" electrons.
"Real" electrons are not at one point of the orbit, but within a certain volume, at best. Due to uncertainty (Heisenberg was not that off-topic after all), one cannot determine both velocity and location of an electron. Pinning the location down to a volume smaller than the apparent radius of the orbital would allow for velocities sufficient to escape the atom; that measuring method would give us a good location but ionize the atom in the process.
The orbital can "move" (it can snap towards other atoms and blend with their orbital), but it doesn't move with the electron. The point of the orbital is to relate each possible location to the probability that the electron will be nearby. s-prbitals are spherical, but p-orbitals are not.
Electrons change orbitals when they receive or lose the right amount of energy. That's the very principle of emission. absorption, and spectral analysis: different atoms mean different energy levels, thus different frequencies (E = h f, h being Planck's constant). - ¡Ouch! (hurt me / more pain) 07:52, 11 January 2013 (UTC)[reply]
That sounds like someone has been recycling the balls from the stick and ball models of molecules. I've not heard of a code like that for elementary particles but it possibly could be useful in diagrams. Dmcq (talk) 22:40, 12 January 2013 (UTC)[reply]
Is Anthropogenic Global Warming falsifiable?
I had an epistemological question which has to do with the fact we probably can't reverse the continuing increase of greenhouse pollutants which are posited to be the inextricable causes of global warming, thus losing the chance to conduct an experiment to determine whether reducing our greenhouse emissions will lead to a cooler climate. If anything were possible, we would create a perfect clone of earth and make everyone live 100% perfectly "green" while this earth continues the status quo, thus a replicable experiment that can be repeated dozens of times with identical outcomes that would be unassailable.
Background from here it says "NOAA: 2012 was warmest year ever for US, second most 'extreme'" & it is reasonable to say that both "global warming" is going up & so are the "greenhouse pollutants" going up also. However, correlation does not always imply causality.
I used to be a non-believer of AGW due to this page and also because of the climategate scandal, but now that I'm beyond the politics & the election is over, I can finally ask my question here on the reference desk without people bashing mitt romney or republicans (knock on wood!)
So here is my honest, legitimate question: do the 95% of scientists who are in concensus that AGW is real & caused by humans and/or meaningfully exacerbated by humans even though the earth might be warming as we speak if humans were all dead--do those same zealous scientists have weather predictions they definitively stand by? (such as 6 outta the next 10 years will be hotter than any of the last 100 years unless we cap greenhouse gases)
I'm agnostic now about AGW and do not feel like I can learn anything more from wikipedia about AGW after reading the articles without asking for some human assistance from those at the ref desk knowledgeable about the epistemological basis for how do we know what 95% of scientists believe. This is also a chance to share knowledge with someone who is ready to listen to someone on the pro-AGW camp of Wikipedians. Thanks in advance for any answers or book recommendations or online resources that are provided. Bests, the Tomato expert1 (talk) 19:03, 8 January 2013 (UTC)[reply]
The short answer is yes. However, many of the most publicised predictions are ones which, if they come true, will mean that we are already too far gone. I would be interested in shorter term predictions such as you suggest. Personally I am fairly firmly convinced of AGW, but that's mostly on the basis of retrospective studies. I am therefore interested in the short- to medium-range predictive power of the theory.
However, as a former student of chaos theory, I'm bound to observe that the weather is an intrinsically difficult subject, and so a prediction being met would not absolutely guarantee the theory, nor would a prediction being missed completely falsify it. As using less power is cheaper than using more, and we are running out of fossil fuels anyway, I find it pragmatic to act as though the theory were watertight; I don't think I can reasonably lose out that way. AlexTiefling (talk) 19:13, 8 January 2013 (UTC)[reply]
PS: Delingpole's critique is not based in science, but in a frankly paranoid conspiracy-theory view of the scientific community which cannot reasonably be taken seriously. This response [7] to his blog is instructive. AlexTiefling (talk) 19:18, 8 January 2013 (UTC)[reply]
Firstly, I think that our use of vocabulary here is crucial. The greenhouse gas emissions problem is not about "weather" - it is about "climate" - the difference is crucial. The overall climate of the planet changes fairly slowly and somewhat predictably. Weather is chaotic (in the mathematical sense) - so no prediction of weather change is either proof or counter-proof of anything very much. The word "warming" in the term "global warming" is distracting because the weather in some places in the world will not experience a temperature increase - and might even feel a decrease (eg if the north atlantic conveyor current reverses) - and people can only directly experience "weather" - you need a ton of complicated science and statistics to measure "climate". So it would be better to stick with "global climate change". Furthermore, climate change is only one result of the prediction of the effect of greenhouse gas increase - others include sea level rise, loss of arctic and antarctic ice, the diminution of glaciers and so forth, increased chaos in the day-to-day weather of most of the world. Obviously these effects are all inextricably linked.
Equally obviously, the climate change prediction of greenhouse gas emission increase is falsifiable. If we went for 100 years with the average temperature of the atmosphere decreasing steadily while greenhouse gas emissions continued to increase - then the theory would be proven false. This most certainly isn't a matter of falsifiability. It's a matter of whether the theory is true or false. (Being shown to be true or false is not related to the issue of falsifiability. An unfalsifiable theory is one such as the existence of God. We can't prove it false - there is simply no conceivable way to do that. We also can't prove whether we live in a computer simulation of the universe - that's also unfalsifiable.)
So we are beyond falsifiability. It's climate change due to greenhouse gas emissions is falsifiable...for 100% sure.
The important question for unbelievers is now "Is it false?" - which is not at all the same thing as "Is it falsifiable?"
The question of whether predictions have been made that came true is one solid way to show that some theory is likely to be true. So one prediction is that average temperatures around the world would increase...and they have. Another is that polar ice would retreat - and it has. Another is that migratory animal species would live at latitudes increasingly far from the equator - and they are indeed moving that way. Yet another is that while the climate would slowly warm, the actual weather would become more extreme, and that too is clearly true. So there are a TON of predictions that are playing out - and they are fairly consistent in showing the truth of the theory.
But it's extremely hard to prove any scientific theory beyond all doubt. After all, there is always the possibility that some extremely powerful extraterrestrial being is dead set on messing with our heads by screwing with our experimental equipment. You can't absolutely, 100% prove or disprove anything. That's really why this rather vague-sounding word "theory" is used in the sciences when "fact" would have a nicer ring to it. In the end, we have to say "With all that we've looked at - is the balance of evidence that we should take extreme emergency measures to combat the release of greenhouse gasses?" - and to that level of satisfaction, there is no longer any reasonable doubt that global climate change is real and that emissions of CO2 and methane that we have made are by far the biggest culprit.
Sure, we might be wrong (I'd give it a one in a thousand chance) - but the consequences of cutting emissions drastically when we didn't need to are so vastly less than the consequences of inaction if we're correct, that if there were even a small chance that we're correct, then there really shouldn't be any doubt as to the smartest course of action for all humans everywhere.
Oh - and your figure of 95% of scientists believing in climate change is out of date. In 2011, the percentage of scientist believers was over 97%. More importantly, the few percent who did not express belief were not necessarily saying that they actually disbelieve - merely that they aren't convinced yet. The number of scientists who actively disbelieve is down below the threshold at which it can be reasonably measured.
...Just to add, a number of scientists quibble over minutia of details and definitions. So, they may be "skeptical" about certain statements; or they may "disbelieve" certain conclusions; but it would be inappropriate to say that they do not believe in climate-change or human effects on climate. My take is this: "anthropogenic climate change" is not a hypothesis: it is not a statement or prediction that can be tested; so it's invalid to call it "true" or "false;" or even to say one "agrees" or "disagrees" with it. You might as well ask if a scientist "agrees" with impressionist painting, or whether "impressionism" is falsifiable. This phrase, like "anthropogenic global warming," encompasses an entire field of study, a roughly-agreed-upon body of known work, and a whole bunch of opinions about those works; the name of the field is not, in itself, an assertion or prediction that can be tested. A better question should be used to query a scientist's position, or their confidence in the evidence. For example, "to what extent do you believe CO2 concentration determines the total warming?" The response to that type of question would be a scientist's evidence-based opinion; or a statement of fact; or a hypothesis that could be proven true or false. Nimur (talk) 20:50, 8 January 2013 (UTC)[reply]
Also "believing in climate change" needs to be defined. The number of scientists that believe that it isn't changing is smaller than the number of scientists that believe that humans have little do with it, which is smaller than the number who believe that climate is changing and humans are largely the cause but don't believe that it is stoppable, which is smaller than the number who believe that climate is changing and humans are largely the cause but don't believe that it is stoppable by the US and Europe if China, India, Africa and/or South America don't cooperate.
1) Most scientists prefer to call it "global climate change" rather than "global warming", as a few spots may actually get colder (like Northern Europe, if the thermohaline circulation fails).
2) Random variations swamp out long-term effects in the short run, making it quite difficult to predict the climate for the next few years. Only the long-term trends can show changes regardless of these random events. StuRat (talk) 21:05, 8 January 2013 (UTC)[reply]
Climate scientists definitely do have quantitative climate predictions, and you can help with the prediction yourself. See this distributed computing project, which also includes links to some of the papers they've published.
The question of falsifiability is not as simple as asking whether you can do a controlled experiment. Obviously it's not possible to create another Earth to see whether carbon dioxide is the cause of warming, just like it's not possible to create another solar system to see whether Mars' orbit is due to gravity. All we can say is that we have a model of gravity that worked in the past, there's no reason to suspect it wouldn't work for Mars, and it correctly predicted where Mars would be for millenia, so it's reasonable to trust the model's predictions of the future. Climate is vastly more complicated and harder to predict than gravity, not to mention we have much less data to work with, but the essence of climate modelling is to find a physically reasonable model that accurately explains the past climate and apply it to predict the climate 20 years from now. In 20 years, the model could easily be proven wrong--if the global climate was predicted to increase by 1 degree but instead decreased by 4, a change that's easily measurable with modern instruments, the model is inaccurate. --140.180.245.22 (talk) 21:45, 8 January 2013 (UTC)[reply]
To elaborate on Steve's points above: The crucial bit is the difference between weather and climate. Weather is a chaotic process, and looking sufficiently far into the future, weather (say the weather in 3 weeks time, or even whether next summer is going to be a hot one) is essentially random. No person, scientist or not, can predict the future. Climate on the other hand is aggregated weather. Climate is the likelyhood of having a particular type of weather. Mathematically, climate is the probability distribution of weather. The crux is that even if the individual events are random/unpredictable, the probability distribution itself is not random and we can build fairly robust models for it. Robust enough that these can be falsified, given enough data. A single data point (like the US average summer temperature in 2012, or a cold spell in Russia) is not going to tell you anything, but given 20 or so years of observations, you can make quite firm statements such as the likelyhood of seeing this pattern without climate change would have been unreasonably small. Much depends how you define unreasonable, but given enough data you can falsify (or proof) at any threshold level. So yes, climate change certainly is falsifiable. A more interesting question is whether it is falsifiable or provable with the data we are able to gather before it is too late to take action. I fear the answer is probably not. As to whether scientist can make weather predictions that they can definitely standby: No, certainly not. Probably never. Weather is random, chaotic, too complex for predictions. But that's not the fault of the scientists and certainly not a fault with global warming. It is just the nature of the beast. Predictions about climate are entirely different. 86.185.161.4 (talk) 00:05, 9 January 2013 (UTC)[reply]
Note also that different parts of the AGW theory make quite specific and testable predictions. We can directly observe the changes in the infrared spectrum of earth caused by atmospheric CO2 using satellites like IRIS. We can measure the Suess effect to confirm the fossil sources of CO2. And so on. --Stephan Schulz (talk) 13:54, 9 January 2013 (UTC)[reply]
The way to think about the relationship between climate and weather is what many other sciences call principles of mass action. In chemistry, for example, the position and specific motion of individual molecules are not predictable, but that doesn't mean we can't describe the properties of a substance. The properties of a steel canister filled with oxygen are extremely well understood and consistent, though the specific motion of a specific molecule of oxygen is not. It's the exact same way with weather and climate: in climatology a single year's weather is the "molecule" while climate is the "tank of oxygen". --Jayron3214:01, 9 January 2013 (UTC)[reply]
I think a better question for someone to ask is how much of their money should be spent on various options considering their personal values. If a doctor says you have cancer and there's a 90% chance of you living more than 5 years if you have some operation do you have the operation? I'm sure Delingpole could find lots of surgeons who have botched operations or papers casting doubt on various techniques, does that mean you ignore the doctor or does it mean you take a second opinion? If 9 out of ten doctors say go for it what then? Does a general say "I don't know exactly where the enemy is, therefore I won't do anything"? They try and work out the best thing to do, for a general that might even mean tossing a coin sometimes! Too much of this looking behind by people who are not qualified in the minutiae strikes me rather like this [8]. Dmcq (talk) 15:12, 9 January 2013 (UTC)[reply]
The original question is kind of large and vague for scientific purposes (no offense). But the CO2 greenhouse gas "global warming" model offers numerous points where it can be falsified; like any chain of cause/effect, disproving a single link would disprove the entire hypothesis.
Examine the theoretical model: we're burning a huge amount of carbon that hasn't been in the atmosphere for hundreds of millions of years, burning carbon produces CO2, the additional CO2 will make the CO2 levels in the atmosphere rise, CO2 absorbs near IR energy at the frequencies the earth radiates, the energy absorbed will end up dissipated in the atmosphere, making it not just warmer, but more energetic in general. That overall model could easily be falsified, if any part of that chain were proved false. Setting aside any partisanship here as much as humanly possible, I'd say every step in that chain is pretty well proved past the likelihood of disproof at this point. So, the question of "disproof" becomes one of either providing an additional, equally well established effect that will negate or interfere with this process, and/or (preferably and) demonstrating convincingly that this is not happening in reality. In the absence of either or both, all of the other hypothetical causes of warming offered as "disproof" are irrelevant to the question; just as any discussions of how your house warms up every summer, or the possibility that your house is getting warmer because the furnace is on, become irrelevant to the question of whether your house is getting warmer because it's on fire, once you know that there are actual flames eating your draperies. And the models suggested for effects that interfere with the CO2 greenhouse gas model described above, such as the various iterations of the "higher temps will lead to more clouds which will reduce solar energy absorbance", are so far from being even demonstrated, let alone proved, at this point that they may be dismissed as handwaving; and the kind of evidence cited to demonstrate that in reality the model isn't functioning, such as "it hasn't warmed in the last 2/3/4/8/whatever years" don't meet any standard of evidence either, given that literally dozens of similarly sized flat periods can be demonstrated in the process of the unequivocally rising temperatures of the last century. Thus, yes, the theory is quite falsifiable, but nothing so far has come anywhere near falsifying it. Gzuckier (talk) 04:49, 10 January 2013 (UTC)[reply]
Doubling the carbon dioxide only has a small effect in absolute terms because most of the effect already happens - the climate skeptics are right about that - but what they then fail to take into account is that temperatures are not relative to zero degrees Centigrade, they are relative to absolute zero which is -273°C. The changes we're talking about like 2-5°C are quite small compared to that. Everything being small in absolute terms and the overall complexity makes it difficult to calculate the effects accurately but there is no real doubt about the general outcome. When a thermostat is turned up you need to show something like that a door has been opened and that it is cold outside to avoid the conclusion that the house will warm up. Dmcq (talk) 14:35, 10 January 2013 (UTC)[reply]
How Ears and Eyes Extract Frequency?
I know that we can extract frequency information from raw signals using methods such as FFT, but how do our organs do it without any apparent computation?
75.228.142.113 (talk) 19:50, 8 January 2013 (UTC)[reply]
For the eye: most studies indicate that the extraction of spatial frequency is performed in the brain, not the eyeball. This naturally becomes pretty complicated in a hurry; but you can start by reading this website, the "Cornea Lab" in the Vision Science Program at Berkeley; here's a good starter paper, on spatial frequency selectivity of human vision; it cites dozens of books and papers for background reading. The extraction of frequency of light - in other words, color, is performed inside the specialized cells of the human retina: what we commonly call the cone cell. These cells contain photochemical that makes them selectively receptive to photons of specific color (frequency of light).
Finally, you might be surprised at how straightforward it is to build a discrete cosine transform to extract spatial frequencies out of a focused optical system. This can be expressed mathematically through the framework of Fourier optics. A fast fourier transform isn't necessary, because such machinery works in the analog domain and does not depend on sequential digital calculations. You can extract spatial frequencies simply by intelligently combining signal levels from various combinations of the input (i.e. the retina cells) when stimulated by a focused image. This is the exact analog representation of computing the inner product of the image against each basis-function in the transform domain. Nimur (talk) 20:15, 8 January 2013 (UTC)[reply]
For the eye, we have to be careful to distinguish the frequency of the light from spatial frequencies and even temporal frequencies (eg strobe lights).
The light frequency isn't measured at all well - at least not compared to the ear. We have three kinds of color sensors that detect light as amount of energy within a range of frequencies with a roughly gaussian fall-off. The center frequencies of the three kinds of cell are at the colors Red, Green and Blue. We perceive pure yellow light (eg from a sodium lamp) because both the red and green detectors are producing a mild response and the blue is not. However, to use an acoustic analogy, a "chord" of red and green light looks exactly the same as yellow light - we literally can't tell the difference. It's as if a chord of the C and E keys on a piano sounded exactly the same as the D key by itself! Another set of cells detects the overall brightness of the light and is more sensitive to motion.
The spatial frequency appears to be an ugly mixture of pre-processing in the retina and post-processing in the brain. There isn't enough bandwidth down the optic nerve for each cell to report back to the brain individually - so we know that there is a considerable amount of pre-processing going on in the retina. We know that edge-extraction happens in the retina - and that's a component of frequency analysis. Everything is very much complicated by the fact that our eyeballs continually vibrate in their sockets - this scans the scene with the retina to eliminate "pixellation" such as you get with a TV camera. If a camera with the same number of pixels as the retina is used to take a picture, you can see the individual pixels - but the eyes don't do that because of this vibration. That increases our spatial frequency perception beyond the resolution of the retina. When your eyes get tired (or you get drunk!) this vibration ceases and your vision goes blurry - that blurry vision is the "natural" resolution of the eye. All of this complication greatly enhances the difficulty of answering this kind of question!
Temporal frequency is another strange thing. We don't see single "frames" of video like a TV or a film projector - instead, we're getting signals from the retina like "An edge, sloped at 45 degrees is moving left to right at such-and-such speed"...but it's not a discrete time-sampled signal - which is why we don't see strobing and temporal aliassing in normal daylight.
Interpreting the way the eye works as an analogy of a digital camera is a very bad idea! The entire system from the mechanics, the optics and the image-processing "circuitry" works totally differently to any man-made camera. SteveBaker (talk) 21:12, 8 January 2013 (UTC)[reply]
"The center frequencies of the three kinds of cell are at the colors Red, Green and Blue" is false, as I and others have pointed out to you repeatedly in previous threads. As shown here, two of the cone types are maximally sensitive in the yellow-green-cyan range, and the third peaks in the violet.
The claim that microsaccades increase the eye's effective resolution doesn't seem to be backed up by the article. The eye, unlike cameras, has a fovea, and we can see any small part of a scene in great detail by pointing the eyes at it, but those are large eye motions, not tiny vibrations. Everything outside the fovea is very blurry. The smallest microsaccades (according to the article) move about 2 arc minutes, which is several times the separation of photoreceptors at the center of the fovea (about 0.5 arc minutes).
"When your eyes get tired (or you get drunk!) this vibration ceases and your vision goes blurry" is wrong. The actual cause of the blurred vision (and seeing two of everything) is a failure of accommodation. -- BenRG (talk) 23:18, 8 January 2013 (UTC)[reply]
"The light frequency isn't measured at all well." True indeed. I was lucky enough to attend one of Edwin Land's lectures on his retinex theory, and he demonstrated that photographing a scene with red and green filters, then projecting those two B&W slides with two narrow wavelength yellow lamps whose wavelengths were 10 nm apart, resulted in perception of the full spectrum of colors, although at that degree of closeness the colors were definitely on the washed out side. But, perception of blue and red when the only light sources were both yellow? Definitely vision does not measure frequency of light the same way the ear does sound. Gzuckier (talk) 05:07, 10 January 2013 (UTC)[reply]
You may find chroma subsampling interesting, as well. Not only is the eye interpolating information about what color it sees; it also is very imprecise in where it sees each color. This is one reason that JPEG or MPEG compression, or even analog signals bearing ATSC television data, are so efficient from an engineering standpoint: because the human vision system is very easily fooled by very deviant reconstructions! The easiest way I can visualize this is to consider watercolor painting. If you look analytically at a sample painting and observe where the colored portions are, you see that they aren't where they should be! Cézanne can't even keep his brush inside the lines! But if you step back, the painting looks strikingly "realistic," even though the colors are in completely the wrong place - and who ever saw a purple human! Alas, it's easier to be an artist than an engineer... those guys can get away with anything!Nimur (talk) 04:30, 11 January 2013 (UTC)[reply]
Here's the article's source: [9]. I don't see an upper limit. If all the liquid nitrogen has evaporated, this may leave a small quantity of near 100% liquid oxygen (with maybe some dry ice and water ice mixed in). StuRat (talk) 22:37, 8 January 2013 (UTC)[reply]
That was actually my follow-on question, you mind reader you. Can someone else just confirm this: if I leave a bottle of liquid nitrogen in the open, it'll become a bottle of liquid oxygen (with impurities) at one point.Dncsky (talk) 22:56, 8 January 2013 (UTC)[reply]
I missed "at one point" in that sentence. I've added it now. I'm basically asking for a confirmation on what StuRat said. Dncsky (talk) 23:53, 8 January 2013 (UTC)[reply]
I'm not even sure that's the case, except in carefully controlled conditions, where the ambient temperature is below the boiling point of oxygen but above boiling point of nitrogen (between the window of 77 K - 90 K). At room temperature, trace amounts of liquid oxygen are probably forming within the liquid nitrogen, but these probably boil off along with the nitrogen, to the point where it never makes up a significant portion of the liquid. --Jayron3201:30, 9 January 2013 (UTC)[reply]
Doesn't that contradict the article though? It's saying "increasingly enriched in oxygen", but you're saying it's just trace amounts. Maybe I'm misunderstanding what the article meant.Dncsky (talk) 02:30, 9 January 2013 (UTC)[reply]
(edit conflict)You'd need some special geometry of your container to get a noticeable amount. Boiling (i.e., evaporating) LN2 has N2 gas streaming off of it, which makes it hard for much room-air (source of O2) to reach the LN2 and condense in. I've left LN2 dewars and flasks open until it's all gone, and I usually have little if any water-ice in the bottom even in humid labs, but I do get water condensing on the still-cold glass surface after the LN2 has evaporated. DMacks (talk) 01:31, 9 January 2013 (UTC)[reply]
Actually, what DMacks reports is true only under limited (but very common) circumstances. Often, the evaporating LN2 pushes all O2 away from the surface, which can fool you into thinking it always works that way. If you have a container with a wide mouth and a cross-breeze you will definitely end up with all the LN2 boiled away and a smaller amount of pure LO2 in the container. Also, if you put LN2 in a regular (non-dewar) metal container, LO2 will condense on the outside, as seen here:
"Liquid nitrogen will condense oxygen from the air. This is most alarmingly demonstrated if a person leaves his/her vacuum pump's coldfinger in a Dewar of liquid nitrogen overnight. In the morning the coldfinger will contain LIQUID OXYGEN up to the level of the nitrogen in the Dewar." --Guy Macon (talk) 11:28, 9 January 2013 (UTC)[reply]
Thank you very much, Guy! After reading the LN article I just thought to myself: "How cool is it that when I leave substance A out in the open it'll turn into substance B! And B isn't even chemically derived from A in any fashion.". StuRat confirmed my suspicion and how you found the source to back it up. Thanks again. Dncsky (talk) 18:55, 9 January 2013 (UTC)[reply]
Rainbow colored clouds?
I was just on my way home from work today and in the south-western part of the sky, there was a cloud that appeared to be in the colors of the rainbow - yellow, red and faint blue in that order from right to left. The Sun was to the right of the cloud. I've seen plenty of rainbows before, but they accompany rain and span across the sky. There was no rain (that I am aware of) and it was localized in a very small area of the sky - just a portion of some clouds. I observed it for a good 10-15 minutes at least.
I tried to take pictures of it with my cell phone, but I was driving and it was almost impossible to keep the Sun out of the frame. I can try to upload a picture to Commons if any of them came out alright.
So, here's my question: Can anyone tell me what I just saw? I can't recall ever seeing anything like this before.
In case it helps, this was in the Chicagoland area and it was about 4pm local time.
A Quest For Knowledge (talk) 22:54, 8 January 2013 (UTC)[reply]
Sunset was at 4:37 PM in Chicago today [10], so the Sun was low in the western sky. I suspect there was some distant rain, which the sunlight shone through, causing it to be diffracted, before it struck the clouds. Looking at a weather map, there does seem to be rain coming in from the West, so perhaps that was the first little sprinkle. StuRat (talk) 23:58, 8 January 2013 (UTC)[reply]
A rainbow is water droplets glistening in the sun. The physics determine that the colour they appear to you depend on the angle formed by the sun, the water droplet and the observer, creating the illusion of the rainbow. It does not have to be falling water, but can be mist, fog, or even clouds given the right conditions. The rainbow article has pictures of quite a few different examples. 86.185.161.4 (talk) 00:19, 9 January 2013 (UTC)[reply]
Likely to be substantially colder at cloud elevation. I was thinking of CZA, too, given that the sun was low in the sky and the mercury was low as well. -- Scray (talk) 01:01, 9 January 2013 (UTC)[reply]
My copy is buried somewhere as a result of moving, but what you saw is almost certainly described somewhere in The Nature of Light and Color in the Open Air: Minnaert covers just about every atmospheric optical effect in it. --Carnildo (talk) 04:03, 9 January 2013 (UTC)[reply]
Hmmm...well, there was no discernable arc to the rainbow and it was a very, very small portion of the sky. Anyway, I Googled (well, Binged) for images this morning (I have no idea why I didn't think of that last night) and here's a few that are kind of what I saw.[11][12][13]A Quest For Knowledge (talk) 14:31, 9 January 2013 (UTC)[reply]
OK, here's one of the pictures I took yesterday. You can barely see the colors of the rainbow and it looks a lot brighter than it did yesterday. In fact, it kind of looks like a comet or a UFO. The Sun is on the far right, and the 'rainbow colored cloud' is towards the center (slightly offset to the right).
@Wnt: I'll through that list you mentioned previously as soon as I get a chance, but as far as it being a sun dog, it is at the same height as the Sun and the red part of the rainbow was facing the Sun. But there was no halo effect. A Quest For Knowledge (talk) 13:00, 10 January 2013 (UTC)[reply]
January 9
a map showing the international date line in the middle
I would like to be able to see a world map with the international date-line more centred. (in one piece) - ie: i do not want to see part of the one side of the date-line SQUEEZED in on the right- and the other part SQUEEZED in on the left of the whole image/picture/diagram.
Looking at an existing time-zone map of the world, a more convenient split would be somewhere between 30 to 60 (degrees) West longitudes - as this looks like a longitudinal zone with the least breaks or "zig-zags".
How many times can a hand grenade realistically bounce off a wall before either coming to a stop or exploding, whichever comes first? Assume that: the grenade in question is a German stick grenade with a standard 5-second fuse, thrown at the wall at a 45 to 60 degree angle as hard as possible; the thrower is tall and has long arms but only average strength; and the walls are concrete and about 3 feet apart, forming a narrow passageway. 24.23.196.85 (talk) 06:46, 9 January 2013 (UTC)[reply]
It could only bounce of a wall once. If you mean bounce between two walls, that would depend on how high along the walls it hit initially, it's angle relative to the ground, and it's initial speed. The don't bounce very much, so it would have to be going quite fast to bounce more than once or twice. StuRat (talk) 06:53, 9 January 2013 (UTC)[reply]
It still depends on the width of the passageway (imagine a passageway 100 feet wide - there could only possibly be one bounce...now imagine a passageway only a foot wide - and there would obviously be many bounces)...also the height at which the grenade initially hits the first wall...if it hit the first wall very low to the ground then fewer bounces than high up. Then we need to know the speed of impact, the angle of the impact...there are just far too many variables.
Worse still - they have a very irregular shape - how it hit (stick first, head first, sideways) would make a massive difference. The rate and direction of rotation would add a complicating factor. Also the head of the grenade was very thin metal - it would likely dent easily - absorbing energy from that first bounce and drastically reducing it's speed. But if the stick hit first - it's wood, flexible like a very stiff spring - so it would probably retain most of the energy providing more rebound.
If you want to get even more technical - our article says that the 1942 and later versions had a serrated steel sleeve that could be optionally be slid over the head to get a greater fragmentation effect in anti-personnel applications - which would really complicate matters in a head-first impact because the serrations would result in a much more random bounce/spin.
Gut feel says "once"...or maybe "not at all" - but there are too many variables to come up with any kind of informed answer.
If I were you - I'd take a foot of broom-handle and firmly duct-tape a 500g can of soup to the top - then get out there and try it! Nothing short of tossing one around yourself will give you the authentic "feel" you need for how they would bounce.
Not soup. Anything liquid will slosh and act as a damper. Something solid enough to not slosh when you shake it is better. A can of chili or dog food should do the trick.
I am guessing that straight on to the wall will give you maybe a one foot bounceback, but a glancing hit will retain most of the velocity -- but make the next wall effectively farther away, so maybe two bounces. I really want to see pics of this. Do it! Do it for SCIENCE!! <smile> --Guy Macon (talk) 15:56, 9 January 2013 (UTC)[reply]
Good point about the liquid thing...but most regular cans are only about 250 to 350 grams - I was thinking specifically of the larger diameter cans that might weigh more like the 560 grams that the real grenade weighed...minus the weight of the stick...so a 500g soup can would have about the right weight. I've seen dogfood in those larger cans though - that would work. SteveBaker (talk) 17:31, 9 January 2013 (UTC)[reply]
@24.23.196.85, are you asking this because you want to incorporate it into a graphic novel, film script, story, or other work of fiction? If so, one, maybe two bounces would be the limit of "realistic". But if you're going for exaggerated violence a la Tarantino, have it bounce as many times as you want! - LuckyLouie (talk) 16:29, 9 January 2013 (UTC)[reply]
I suspect that one bounce (or possibly no significant rebound at all) is the most likely "realistic" outcome - but two bounces and some rolling would seem "credible" to me - especially in a book where your imagination gets to roam free. It might be harder to make it believable in a movie though. Our article on the later Model 43 grenade suggests a detonation delay of 5.5 to 7 seconds...which might help to extend any exciting rolling and/or bouncing and/or being-"fetched"-by-a-stray-dog deemed necessary for the plot. SteveBaker (talk) 17:28, 9 January 2013 (UTC)[reply]
That was my plan all along -- a bank shot to send the potato-masher behind a partition in order to take out a German machine-gunner. Based on the layout of that particular pillbox, I can do it with two bounces, but I'll have to shorten the partition somewhat to make it happen. :-) BTW, I like the experiment you suggested, but the one thing to which I don't have access is concrete walls 3 feet apart -- all the walls around me are made of wood. Will that make a significant difference? 24.23.196.85 (talk) 00:19, 10 January 2013 (UTC)[reply]
I find it really hard to believe that you'd have the time or information to plan that kind of a trick. Pillboxes had all sorts of internal layouts - and it's hard enough to toss the grenade into the firing slit as it is without having to consider bounce angles and all of that stuff. The stick grenade is particularly ill-suited to that kind of trickery anyway because it's such a weird shape and really off-balance! It's not like you can stand a couple of feet outside the firing slit, examine where the internal walls are, consider the angles, wind up for a really accurate toss with just the right spin, speed and direction! There are a bunch of guys inside who are working very hard to be sure that you don't toss ANYTHING in there! You'd be standing with your back to the concrete wall, with grenade in hand - and consider yourself lucky if you could get the thing inside in any way at all without having your hand blown off! It's also very dark inside those pillboxes - it would be tough to discern anything much about the interior structure from outside. So for me, your story's "credibility" is blown long before we have to consider whether the grenade could physically bounce as intended! SteveBaker (talk) 15:08, 10 January 2013 (UTC)[reply]
I love it. Even assuming a Jason Bourne-like hero, it seems there's a lot more practical issues to consider in this scenario than just 'could a stick grenade bounce twice'. I think the OP might be envisioning a door at the back of the pillbox with a partition separating the entryway from the front gun port area. Even so I'm sure it has a metal door the German crew keeps closed. But let's say the door is open or blown off. Much easier to shoot the guard (if there is one) and then run inside blasting your Sten gun or whatever, using the partition for cover. Any way you slice it, this is all fantasy, so why restrict fiction to 'what can be tested'? - LuckyLouie (talk) 17:40, 10 January 2013 (UTC)[reply]
Sure, there are times when the needs of good fiction override practical reality. However, when something really ridiculous happens, it can also detract from the story. (I could cite countless movies and TV shows that were ruined for me by some ridiculous - and unnecessary - impossible thing.) So if there is no loss of narrative quality, one should err on the side of real-world possibility. Clearly our OP's careful questioning of such minutia as the color of the handles in the signal box that our hero uses to redirect the train - suggest that this will be a very grounded-in-reality kind of a novel. In that case, surely there is another clever & creative way to take out this pillbox without our hero doing such a truly super-human trick. Perhaps start with a document like this one: http://www.lonesentry.com/articles/pillboxwarfare/index.html - which describes how US soldiers would approach a pillbox. It provides the valuable advice that a white-phosphorus grenade is more effective against a pillbox than a fragmentation grenade. But it also adds crucial advice about NOT attacking the rear door and that intersecting fields of fire from adjacent pillboxes is a major threat. There is a lot of scope for our hero to be heroic beyond having the ability to bounce a weird shaped grenade off of half-seen walls through a small slit. SteveBaker (talk) 18:12, 10 January 2013 (UTC)[reply]
Not a small slit -- a bent entrance-type passageway that serves as the entry point for the pillbox, which is covered by an MG-42 emplaced in a gunport in the partition around which the passage doubles-back (which machine-gun has to be taken out because it also covers main route of advance). In effect, the passageway leads up a short staircase toward the wall with the machine-gun, then makes a 90-degree left turn for a slightly shorter distance, and doubles back into the pillbox itself. And they don't have to worry about interlocking fire because it's a stand-alone pillbox covering the entrance to a railroad cutting. (If you like to play the Medal of Honor: Allied Assault computer game, at one point you encounter a similar situation in the Normandy level.) 24.23.196.85 (talk) 02:29, 11 January 2013 (UTC)[reply]
Just read the document -- what it says is, rather than not attacking the rear door at all, that the attacker must not stand directly in front of it, because there's always a machine gun covering that sector. But that's not my plan in the first place -- I'm not so stupid as to have my hero stand right in front of the doorway in full view of the machine-gunner. That's why I asked about bouncing the grenade off the walls, because the assault team will have to throw it in while standing to one side of the doorway (which means they're throwing essentially "blind") and try to have it it bounce around the corner to land behind the partition. 24.23.196.85 (talk) 02:44, 11 January 2013 (UTC)[reply]
Does it really matter that it's a stick grenade? The German army also issued "egg" grenades (Model 39 grenade) - and it seems much more credible that one of those would bounce and roll around much more than the ungainly stick models. The article on the Model 24 grenade actually says that one of the benefits of the stick design was to prevent it from rolling on hilly terrain - so if the plot requires that the grenade take some complicated path to it's target - then an egg grenade would be a better choice. SteveBaker (talk) 17:44, 9 January 2013 (UTC)[reply]
I presume they'd be "liberating" those weapons from the Germans along the way...how else would they have gotten hold of the stick-grenade variety? If they stole the weapons somehow - then they'd be likely to find an occasional "egg" grenade along with the "stick" variety. But if they did that, they'd have to be careful - one sneaky trick the Germans employed when retreating from a position was to swap out the 7 second fuses for 1 second fuses and leave the grenades lying around for the enemy to pick up and attempt to re-use! Yikes! (Of course the hero in a novel would likely know all about this trick and be prepared to re-fuze the grenades before attempting to use them!) SteveBaker (talk) 15:08, 10 January 2013 (UTC)[reply]
Hey, that's an interesting idea -- maybe Blanche's jealous ex-boyfriend will acquire some instant-acting Model 39s from a crooked arms dealer and give them to Mike, hoping he'd blow himself up? ;-) 24.23.196.85 (talk) 02:49, 11 January 2013 (UTC)[reply]
Hmmm - our article Maquis des Glières and Maquis du Haut-du-Bois both say that the British air-dropped large numbers of "mills-bomb" grenades for the use of the Maquis. (One drop is mentioned as containing 150 grenades). So they most certainly did have 'egg'- and 'pineapple'-style grenades. It's entirely possible that they used the stick variety if they could steal them from the Germans...but the British hadn't made stick grenades since 1908 so whatever the Maquis got in air-drops in 1944 would have been "pineapple" fragmentation grenades for sure. It seems unlikely that the Brits would have air-dropped grenades if the Maquis had a good supply of German grenades - so it seems highly likely that pineapple grenades would have been in the majority. Whether they'd prefer stick grenades over pineapples is debatable - stick grenades can be thrown further - but they are a pain to transport and difficult to use in confined spaces. For taking out a pillbox with a fancy rebounding throw, a pineapple grenade would be greatly preferred. SteveBaker (talk) 15:36, 11 January 2013 (UTC)[reply]
1) Kind of. If the horizon is absolutely flat, then yes. However, hills or mountains or even snow drifts mean that as the Sun corkscrews up and down it will pass behind them and then come back out, so you will get multiple "sunsets" and "sunrises".
2) It's so cold in summer because the Sun is at such a shallow angle. In winter, it's far colder because there's no sunlight at all, for months at a time. Also, prevailing wind direction is East-West, meaning very little warm air moves in from warmer areas. StuRat (talk) 08:14, 9 January 2013 (UTC)[reply]
At the south pole east is clockwise when looking down and west is anticlockwise. Opposite at the north pole. So in winter time you will not see stars rise in the east and set in the west, but they will just circle you. The point is that the wind does not go towards you to carry heat from outside. Graeme Bartlett (talk) 20:24, 9 January 2013 (UTC)[reply]
That's the point, the winds blow in a circle around the poles (more or less), not over them, where they would deliver warmer air. StuRat (talk) 20:21, 9 January 2013 (UTC)[reply]
So in summer, the sun is at what angle? How low is it? So if the sun will not set, we can see the sun 24 hours a day and we will see it circling in the sky? roscoe_x (talk) 00:43, 10 January 2013 (UTC)[reply]
When the sun is directly above the equator, it appears from the North Pole at the horizon. At the height of summer for the Northern Hemisphere the sun is about 23° north of the equator, so when standing on the North Pole the sun will be seen circling between 0 and 23° above the horizon (i.e. in the summer season). - Lindert (talk) 09:36, 10 January 2013 (UTC)[reply]
Just to clarify that last sentence of Lindert, on any one day the sun will circle at a particular number of degrees above the horizon. That number of degrees will be about 23 (closer to 23 1/2 actually) at the summer solstice, and it will be zero degrees at the autumnal equinox and at the spring equinox. As the days go by after the spring equinox and as we get closer to the summer solstice, the number of degrees above the horizon increases from one day to the next.
Here's how to visualize things like this. Get a globe, which will be tilted at 23 1/2 degrees. Put it on a table top so that the interior center of the globe is a certain height above the floor. Hold a thin flashlight (a penlight)(representing the sun) at that same height but some distance away and shine it at the north pole. Spin the globe around to see what is happening during the course of one day. To show the summer solstice, shine the penlight toward the globe from the horizontal direction that the top of the globe is pointing toward. To show one of the equinoxes, shine the light from the same height but after you and the penlight have moved 90 degrees around the globe. You can also look at in-between dates using in-between locations of the penlight. Duoduoduo (talk) 20:16, 10 January 2013 (UTC)[reply]
So the phenomenon is called midnight sun. Okay, so the people in north pole still know the time of day (even at night) by looking at the sun's position relative to objects near the observer? And if I built a house in north pole I wouldn't make a window that will pass sunshine at night time. And another question can you see Aurora from the poles? And if North Pole and North Magnetic Pole is different, also its moving, how far North Magnetic Pole can moved from North Pole? If we make an experiment of flowing water in a tank, will it also moving clockwise in the North Pole? Thanks guys, interesting phenomenon and answers. roscoe_x (talk) 01:41, 11 January 2013 (UTC)[reply]
(outdent) You couldn't build a house at the geographic north pole because it's an ever-shifting (and these days quite unstable) ice floe. So telling the time by the position of the sun or stars would actually be quite difficult. I guess you could use the direction of the magnetic north pole (see below) to provide a fixed line of reference, and from that calculate the time of day in any given time zone. In practice, permanent antarctic stations maintain the time zones of their control centres in nearby southern hemisphere countries. As for the windows: obviously during the nearly-six-month polar night, no window is going to admit light anyway. But when the sun is above the horizon anywhere, Rayleigh scattering makes the whole sky pretty bright. So you'd definitely want blackout curtains, or a bedroom with no windows and only artificial light. (I spent two weeks in the Swedish sub-arctic just after midwinter once; the weirdness of the daylight hours got to me pretty quickly.) I believe the aurora can be seen at the pole. The magnetic poles move pretty slowly, but fast enough that (for example) British Ordnance Survey maps include a magnetic north line, with details on when it was computed, and how far it's expected to deviate in subsequent years. However, in the very long term, it's believed by geologists that the north and south magnetic poles change ends, so the current north magnetic pole could end up arbitrarily close to the south geographic pole. And lastly, unless your experiment is very carefully controlled, the shape of the tank will have more effect than the rotation of the earth. (The earth's rotation does not, for example, affect which was water goes down an ordinary domestic plughole.) Our article Coriolis effect has the details - but the south geographic pole would be a slightly easier place to that experiment, and see the real effect of the earth's rotation on the water, than anywhere else on earth. AlexTiefling (talk) 02:07, 11 January 2013 (UTC)[reply]
Why do electrons, nucleons, stars, and planets have spherical shape ?
I have no microscope to observe electrons, protons, and neutrons in an atom, but I satisfy myself by only looking their pictures in books, on Wikipedia, etc. I usually see that they are spherical. Are they really spherical ? If yes, then, why not other shape ? Why do stars and planets have spherical shape, not other shape ? On the other hand, meteorites are not spherical but irregular. Why ? Parimal Kumar Singh (talk) 09:08, 9 January 2013 (UTC)[reply]
For the astronomical objects, gravity is the culprit. Large enough objects have enough gravity that it crushes anything that sticks up. However, if they rotate quickly, the shape is more of an oblate spheroid. For the subatomic particles, I don't think they really have a shape, just a probability density. It's just simpler to represent them as spheres. See probability amplitude for an alternative representation of an electron in a particular atomic orbital. StuRat (talk) 09:20, 9 January 2013 (UTC)[reply]
That isn't the electron. That's the region where the electron might be found. The electron itself, as far as anyone knows, is a point charge/point mass. Maybe something like string theory would make it something other than a point, but no one knows how to test it. --Trovatore (talk) 09:31, 9 January 2013 (UTC)[reply]
I think that's a mistake. Admittedly it's one you see in writing from time to time, but still a mistake. To see the difference, note that, say, protons also have a probability distribution for where they might be found — but if you take that to be the "shape of the proton", then you completely lose the ability to talk about the proton's internal structure, with the three quarks floating around and exchanging gluons. The proton does have a shape, sort of, that being the shape given by the positions of the quarks, and definitely not given by the probability density function for position of the proton as a whole.
So the correct answer to "what is the shape of the electron?" is "no one knows; it might not have one at all", but is definitely not "the shape of its probability density function". --Trovatore (talk) 09:48, 9 January 2013 (UTC)[reply]
Regarding the proton shape: You've still got the same problem as with an electron, insofar as quarks are point particles like electrons, which themselves obey quantum rules and thus have the same problems with concepts like localizability and volume. So, since the "shape" of a proton is dependent on the "shape" and "position" of quarks (which is essentially as meaningless a concept as it is with electrons), so I don't think you can meaningfully discuss the shape of a proton any more than of an electron. Even the nucleus of the atom has a structure and a shape that defies easy definition. The smallest objects whereby shape takes on specific, definable, meaning are atoms and molecules, and even there there is some "fuzziness" (i.e. various ways to define atomic radius). --Jayron3213:39, 9 January 2013 (UTC)[reply]
Well now, hold on. The position of a quark is not "meaningless", it's just quantumly weird. The proton is a quantum superposition of infinitely many states in which all three quarks have precise positions, and each of those states has a precise shape (a triangle, though not the same triangle for each of the states), and where each of the quarks is, as far as anyone knows, a point mass. Anyway I agree that it's the same issue; that was kind of my point. I was explaining why the shape of the orbital is not correctly identified with the shape of the electron. --Trovatore (talk) 18:50, 9 January 2013 (UTC)[reply]
Wait a moment there! Take any three points in space and just try to position them so they aren't in a triangle! That's not "a precise shape"! Literally any position they might be in would be a triangle. (Albeit a "degenerate" one if they lay on the same straight line or two or more of them were at the same position).
Just glanced at it — is there anything there that's inconsistent with the hypothesis that the bare electron is a point mass? If so I didn't see it. --Trovatore (talk) 19:07, 9 January 2013 (UTC)[reply]
No, not yet but I posted that in response to the comment "The smallest objects whereby shape takes on specific, definable, meaning..." to show that people are looking at the shape of smaller objects. Sean.hoyland - talk06:27, 10 January 2013 (UTC)[reply]
The strong force field of protons and neutrons is well approximated by a sphere with a diameter of about 1 fm within which the three "valence" quarks move freely. Electrons are point particles in a sense, but don't forget that the Standard Model is a quantized classical field theory. The quantization leads to pointlike behavior but there's a sense in which electrons can spread out even at the classical level. But unlike nucleons they have no intrinsic size as far as anyone can tell. -- BenRG (talk) 17:32, 9 January 2013 (UTC)[reply]
I'm not sure electrons have a "shape", per se. As far as I know, no one has ever demonstrated that they are anything but pure geometrical points (though of uncertain position). Whether the question even makes sense at all might depend on your interpretation of quantum mechanics.
However, if they do take up space, what shape should they be, except a sphere? Why prefer one direction over another? (They do have spin, so I suppose you could argue for some anisotropy based on the spin vector.) --Trovatore (talk) 09:25, 9 January 2013 (UTC)[reply]
The whole discussion revolves around electrons, most of which is beyond my knowledge. The questions about astronomical objects are not completely answered. Please clarify it. Parimal Kumar Singh (talk) 04:58, 10 January 2013 (UTC)[reply]
Solids are generally held together by chemical bonds. This is the force that gives structure to a rock or an asteroid for example. For small to medium sized solid bodies, the force of gravity is too small to substantially change this. However, once a solid body gets very large (i.e. > 1000 km or so), the gravitational force starts to overcome the chemical bonds and pull it into an approximate sphere. On planets, mountains are held together with the same basic forces that hold together a rock. In general, the larger the planet gets, the greater the gravity at its surface, and the smaller the size the mountains that can exist without gravity breaking the rock apart and causing the structure to collapse. For stars and gas giants, there isn't a solid surface at all. Gravity simply pulls on the gas and it flows towards the center until the pressure of underlying gas can exert an equal outward force. Because the gravitational force is essentially uniform in all directions, the gas also ends up uniformly distributed (i.e. spherical), with small corrections if the object is rotating. Dragons flight (talk) 11:58, 10 January 2013 (UTC)[reply]
Essentially, one can appeal to symmetry. Large objects are only held together by gravity. Gravity is a force that acts equally in all directions - so material will end up uniformly distributed - and the only shape that has this perfect symmetry is a sphere. However, if the sphere is rotating (as is the case for almost all heavenly bodies) - the centrifugal force will be stronger at the points furthest from the axis of rotation - resulting in slight bulge around the equator. So none of these bodies are perfectly spherical.
That said, real planets are incredibly close to being perfect spheres. At smaller scales, such as mountains and such - the atomic forces holding the rock together is stronger than gravity - so more complicated, asymmetrical, shapes become possible. Despite that, the earth is more perfectly smooth and round than a regulation billard ball - and the atmosphere and oceans are thinner than a layer of paint at that same scale. SteveBaker (talk) 14:54, 10 January 2013 (UTC)[reply]
P stands for (electrical) power, i.e. how much energy is used per unit of time (in Watt or J/s); Vc is simply the voltage over the capacitor. - Lindert (talk) 13:14, 9 January 2013 (UTC)[reply]
Where do you see "I" defined as a variable for current in the article? I did think exactly like you until I found it depended on other undefined variables. Electron9 (talk) 19:44, 9 January 2013 (UTC)[reply]
Yes, I was assuming standard symbols there. But also "Power = work per unit time", which seems consistent with the integral form. DMacks (talk) 19:52, 9 January 2013 (UTC)[reply]
Strength of gravity anomalies on earth
The image File:GRACE globe 1.png shows the differences in gravitational acceleration on different parts of Earth, after normalizing the differences caused by the rotation of earth and the polar radius being smaller than the equational radius. But the image doesn't include a legend for the colors, so I can't tell what the red and blue colors represent. So my question is, how large are these variations in the gravitational acceleration? – b_jonas11:23, 9 January 2013 (UTC)[reply]
I have no idea why that was cropped out in the version you refer to!
The scale is in milligals - and the numbers range from -50 to +50, which is 50 thousandths of a 1 cm sec-2 acceleration...normal gravity is around 9.8 m sec-2 and these variations are at most -/+ 0.0005m sec-2 - which is really very tiny! Note that gravity varies by a half percent between equator and pole - so what your latitude is matters vastly more than whether you're standing on a red spot or a blue spot on that map! SteveBaker (talk) 13:45, 9 January 2013 (UTC)[reply]
This site states that there is a 40 month prognosis with AL Amyliodosis, siting a British Medical Journal, without speaking to advanced symptomatic organ failure which accompanies most diagnosis. The actual prognosis of AL Amyliodosis with Cogestive Heart Failure (CHF) is 4-6 months. As it can take 4-6 months for a CHF patient to recieve the Amyliod diagnosis, siting a 40 month prognosis without additional information may lead patients and their families to adopt a wait and see posture early in the discovery process, thus leading to patient mortality. Perhaps someone would like to address this. — Preceding unsigned comment added by 71.232.106.77 (talk) 13:01, 9 January 2013 (UTC)[reply]
You really need to point this out and discuss it on the Talk:AL amyloidosis page where people discuss the content of that article. This is the reference desk - we answer questions and do information searches and such but we don't generally edit articles for people. Right now, I can tell you that the editors of that article are going to want to know where you got your information from. They need a reliable source that they can mention in the article...right now, they're going to say that the British Medical Journal is a highly respected source of medical information - and if it says 40 months - then that's the number they're going to put into the article unless there is another, more recent, reliable source that says otherwise. If you can point to a research paper or some kind of study document - then that will help them to get the article sorted out. But please discuss this on the talk page of AL amyloidosis - the reference desk is not the right place. SteveBaker (talk) 13:24, 9 January 2013 (UTC)[reply]
Because the rubric we learn for predicting the electron configurations is an approximation of reality, and reality is much more complex. --Jayron3214:08, 9 January 2013 (UTC)[reply]
A bit more: The Aufbau principle (aka Madelung's Rule) is a very rough approximation indeed, as it isn't really based on a rigorous mathematical understanding of the quantum mechanics of how electrons interact with the nucleus and with each other to produce a specific configuration. Instead, it is designed as a very rough "rule of thumb" that will get most people the right answer most of the time. There are other, more accurate, approximations , such as the Hartree–Fock method. So the answer is that the reason why copper, chromium, palladium (and indeed many other elements) don't directly obey the Aufbau principle is that the Aufbau principle is wrong, but it's right enough for first year chemistry students to get most elements correct. Indeed, for anyone that never gets to rigorous computational quantum mechanics, the Aufbua principle + memorize the exceptions is usually as far as they will ever get. --Jayron3214:22, 9 January 2013 (UTC)[reply]
Sorry. Aka is an abbreviation for "also known as". The answer to your question is that the method you were taught for determining electron configurations is wrong. Better methods exist, but they involve the sorts of mathematics that 99% of people (indeed, that the majority of chemists themselves) never learn. All methods are wrong (as the quote goes "All models are wrong, but some are useful"), but the one taught you in your chemistry class is more wrong than others. It's right enough, however, for the purposes of your chemistry class, and teaching you less wrong models would require taking several years to teach the mathematics first. --Jayron3215:24, 9 January 2013 (UTC)[reply]
Thank you Jayron, your second explanation was excellent. According to what have been taught in my chemistry class: In chromium second last shell and last shell contain 5 and 1 electrons respectively. On the other hand, second last shell and last shell of copper contain 10 and 1 electrons respectively. Is this true in reality ? Show your knowledge (talk) 15:49, 9 January 2013 (UTC)[reply]
Yes, that is really true. The electron configuration of every element can be determined spectroscopically, such that you can experimentally determine the actual configuration of electrons in an element. The "rules" you are taught in chemistry class (the Aufbau principle) whereby you add electrons to each element based on a simple formula, is mostly right, but it gets certain elements (like Chromium and Copper) wrong, insofar as the Aufbau principle predicts a configuration of 4s23d4 for chromium, but actual experiments have determined that the ground state configuration is actually 4s13d5. There are models better than the Aufbau principle that closer match reality (i.e. models that actually predict the correct configuration of chromium and copper rather than explain them away as "exceptions" to the rule) but those models require a level of mathematics which is well beyond the average first year chemistry student. --Jayron3216:03, 9 January 2013 (UTC)[reply]
I read this in a book: "The deviation (from Aufbau principle) in electron configuration of some elements is because completely filled (d10, f14) or completely half-filled (d5, f7) configurations are more stable. The stability is due to two factors. One, these configurations are more symmetrical which increases their stability. In symmetrical arrangements, the electrons are farthest away from each other, and their mutual shielding is the minimum. The coulombic repulsive forces between them are also weakest. Due to both these reasons, the electrons are attracted more strongly towards nucleus. Two,the electrons in degenerate orbitals can exchange their position. These exchanges also increase the stability. In completely filled and completely half filled orbitals, the number of such possible exchanges are maximum which make such electron configurations more stable." Is this explanation correct ? Show your knowledge (talk) 05:32, 10 January 2013 (UTC)[reply]
Sure. That's pretty much it. There's also probably some small effects from spin-spin coupling of like-spin electrons as well, and larger atoms start to have relativistic effects which affect their configurations. Calculating the exact energy contributions of all of these various effects is quite messy, which is why they don't teach it to you right away, for the most part the Aufbau principle works, except for the "half-filled d" and "all-filled d" exceptions of the copper and chromium groups. There's also other exceptions besides those (there's actually upwards of two dozen of them, at least), and not all of them so easily follow the "half-filled/all-filled" rule-of-thumb, i.e. Ruthenium, Palladium, Cerium, and several more. --Jayron3206:11, 10 January 2013 (UTC)[reply]
Why are all milk frothing mugs made out of stainless steel?
Does milk froth better in a stainless steel container than in a container made of another material (like ceramic)? If so, WHY does milk froth best in stainless steel? — Preceding unsigned comment added by Rmravicz (talk • contribs) 14:16, 9 January 2013 (UTC)[reply]
I assume that you are referring to coffee machines. My home one came with a plastic frothing jug, but I broke it, so now I use a Pyrex one. Both frothed equally as well as the stainless steel ones used in coffee shops. I suspect stainless steel is used, as it is easier to clean than glass or plastic and it won't break when dropped. I also think the professional jugs are doubled walled, so the Barista can froth enough milk for several cups and keep it hot. --TrogWoolley (talk) 15:24, 9 January 2013 (UTC)[reply]
Three questions
1) Why is oxygen necessary for survival? Why not other gaseous element?
2) What make our body to trap only oxygen when we breath in?
3? How long does it take to digest hen meat in our stomach? Sunny Singh 14:21, 9 January 2013 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)
1) The reaction of oxygen with carbon based molecules creates a lot of energy, which we need for our organs and muscles to operate. There is no commonly available gas on this planet apart from oxygen that will perform this function.
2) Our blood vessels contain proteins (hemoglobin) designed to bond with oxygen, thus 'trapping' it, while leaving the nitrogen etc alone. However, they also bond with carbon dioxide and carbon monoxide, so that's why these gases are dangerous in significant concentrations because they take the place of oxygen and so deprive our organs of oxygen. - Lindert (talk) 14:37, 9 January 2013 (UTC)[reply]
The reaction of oxygen with carbon also creates carbon monoxide. Sunny Singh 06:01, 10 January 2013 (UTC)
(ec) 1) Because our bodies produce energy by combustion/respiration, which is an oxidation reaction, and thus requires oxygen. More generally, our biology is based on carbohydrates and proteins, both of which contain significant amounts of oxygen. Nitrogen is also needed, but N2 molecules are very hard to break - no regularly occurring substance burns in nitrogen - so we allow nitrogen-fixing plants (and the animals that eat them, unless we are vegans) to get hold of the nitrogen for us. The other atmospheric gases that come to mind are carbon dioxide, which is a product of respiration, and thus cannot be effectively used in such a reaction, and argon, which as a noble gas is almost (but not quite) impossible to react with anything.
2) The structure of haemoglobin in the blood allows for oxygen atoms to be attached; this takes place in the lungs (roughly speaking). It's not true that we trap only oxygen: for example, carbon monoxide poisoning takes place because the CO molecules bond more readily to the haemoglobin than the oxygen does, and won't come off.
3) As I recall, food (of whatever sort) doesn't stay in the stomach itself more than a couple of hours or so, but takes 24-36 hours to traverse the entire gastrointestinal tract. Digestion takes place throughout most of this period, by several methods. PS: in English, the meat of the hen is referred to as 'chicken'. AlexTiefling (talk) 14:43, 9 January 2013 (UTC)[reply]
(edit conflict) 1) Oxygen is involved in numerous biological processes, Dioxygen in biological reactions covers some of them. But basically, oxygen works by reacting with other molecules to release energy. You can see this dramatically in most combustion reactions, where the oxygen combines with things violently and rapidly to release huge amounts of heat very quickly. In biology, similar reactions are mediated by many enzymes which allow for a slow controlled release of energy that allows every other biological process to occur. 2) Oxygen is trapped from the air by hemoglobin, the specifics of which are covered in the Dioxygen in biological reactions article, in the "Oxygen uptake and transport" section. 3) Digestion#Human digestion process covers the specific timing of various parts of the human digestive process, including the amount of time food spends in the stomach. --Jayron3214:46, 9 January 2013 (UTC)[reply]
nanotube compressed air storage
So, nanotubes supposedly have such high tensile strength just a few molecules wide it can support a space elevator.
Anyhoo forget nanotubes. I'm not sure why I mentioned it. Imagine a sheet of zero weight and infinite tensile strength, and you make a container out of this. You are allowed to pump in air at a small differential to the atmosphere and some kind of mechanism gets it inside, and similarly you are allowed to get air out at the rate you want, magically. However, the container does not have further magical properties, and it is subject to normal laws of thermodynamics. We are just not concentrating on the tensile properties and the mechanism of letting you pump into it and out of it.
So, in this case, what is the limiting factor of how much air you could store in this for use as a mobile power source? Is it the weight of the air? Is it how hot the air inside would get? What happens if, for example, you put a million or a billion cubic feet of air inside?
Basically, I am trying to imagine what happens at the limit of a "perfect container" for storing compressed air.
Now let's turn to practicalities. Practically, what happens to the pressure as you put more and more air in? Where do current known materials have a theoretical limit on how much pressure they can hold? How does the weight of material needed increase in response to the amount of pressure you want? Does something special happen when so much air is put in that the pressure melts it? Freezes it? (What I mean, is would the pressure suddenly spike immensely when you put more air in once the air inside is already liquid, or already solid?)
Forgive me, I assume higher pressure compresses by first liquidizing then freezing the air. Please correct me if I'm wrong.
Now let's turn to the pump. What are the practical limitations on trying to create a pump that you can "easily" pump into and "practically" get power out of in non-explosive bursts, but rather a rate that is more appropriate for driving a car?
Basically, I am trying to imagine what would happen if a nuclear powerplant tried to load a container with several inches of nanotube sheeting with enough air to power a car for ten years. What /would/ happen?
Well before that, the material would be too heavy to transport. Are you saying that with the above assumptions ("infinite container strength and a really, really good pump") the package is already a lot better than gasoline? (Since we can simply stop once we've pumped enough energy into it for it to surpass the energy densitity of gasoline?) 178.48.114.143 (talk) 16:36, 9 January 2013 (UTC)[reply]
You might be interested in the articles Compressed-air vehicle and Compressed air energy storage. In practice, without cooling the container during compression, more and more of the pump energy will go to heat the compressed air (and hence the container, until it melts, or until all the energy of the pump is going into heating the atmosphere round the container). Using cooling, the compressed air can be converted into a pale blue liquid, and that's about as far as it is practical to go since most liquids are very difficult to compress further. Dbfirs17:33, 9 January 2013 (UTC)[reply]
Existing compressed-air cars use air stored at about 50Mpa of pressure and achieve about 1/20th of the energy density of gasoline (so 1/20th of the range for similarly sized "fuel" tanks). You might want to check out Orders of magnitude (pressure) to see what the effect of 1000Mpa pressure would be to get the same range as a gas-powered car. It's considerably higher than (for example) the pressures used to cut steel using high pressure water jets! Actually using that much pressure would be difficult because releasing a 1GPa air flow would destroy anything it hit! To get the pressure up enough to where it could store enough energy to run a car for a year, you're up at pressures where your carbon nanotubes would spontaneously form diamonds and your oxygen would turn into a metal!
It's funny you say that, because I decided to look you up. In the Orders of Magnitude (Pressure) article you linked, 50 Mpa is listed next to 10^7 (the exact exponent would be 7.6), and 1000 Mpa is thus 10^9 (the exact exponent). Well guess what is listed under 10^9: "tensile strength of Inconel 625 according to Aircraft metal strength tables and the Mil-Hdbk-5". So, your very own link shows that storing air at 1000 Mpa is just fine, as long as it's stored in Inconel. So tell me: why not load an Inconel container with 1000 Mpa of air? As for the pump, you can simply make it pneumatic, and out of Inconel, like this: a long tube that tapers. You can then wrap it around the pump or whatever. I've uploaded a diagram. http://i.imgur.com/ksZVB.jpg . I'm not sure if it will work, but I'm sure you'll tell me. I don't see why not... — Preceding unsigned comment added by 91.120.48.242 (talk) 09:28, 10 January 2013 (UTC)[reply]
Inconel 718 is tough stuff - and it is actually used for cryogenic storage tanks - so it's properties in the realms you're interested in are well explored. The stuff is incredibly hard to work with in manufacturing - so the cost of such things would be incredibly high...but our article notes that it can be cut with a Water jet cutter - which you'll note cannot yet reach 1000 Mpa - topping out at maybe 600 to 700 Mpa. So Inconel isn't a magic pressure-resisting-material that you can just assume can be used to make the various parts of your contraption - it's just not that simple!
Moreover, the best pumps available for water jet cutters can only reach 700 Mpa - and that limit is going to apply to your car tank filler. Even if a 1000 Mpa pump, storage tank and turbine were available - the cost of building something like that out of Inconel would be extreme! That's a really expensive, exotic material...and it's very hard to machine - so even if it were possible, the cost of producing a pneumatic car with similar range to a $10,000 Kia would be spectacular - and because this is a fundamental limitation of the material - it's not likely to reduce with large-scale production or technological advances. So your idea - even if possible - is never going to be practically useful.
But the other problem (which earlier respondants have mentioned - but you've failed to consider) is that air liquifies at around 200 atmospheres - which is 20Mpa - so once you get beyond 20 Mpa, you're trying to compress an incompressible liquid - getting even 10% more liquid into that tank would require pressures vastly larger than 1000 Mpa. Hence you can't be using air if you want a car with a longer range than a couple of miles...which is about what real pneumatically powered cars get.
Then you go on to suggest that you can store enough air to run the car for a year - and that's vastly beyond even this possibility.
Steve, thank you for this thoughtful response. In fact the "limitation" (once air is liquid, pumping more in becomes exponentially more difficult I gather - could you show me this on a chart?) was what I first asked about. So, really, your statement was misleading where you suggested "You might want to check out Orders of magnitude (pressure) to see what the effect of 1000Mpa pressure would be to get the same range as a gas-powered car." Because you're saying that, in fact, 1000Mpa are not enough to get the same range as a gas-powered car, because shortly after the 50 Mpa we currently use, the contents are all liquid and increasing the pressure from 50 Mpa to 1000 Mpa hardly gets you a greater volume of gas stored. (If I understand what you are now saying correctly). One thing you did not address however is my pneumatic pump idea: you say "Moreover, the best pumps available for water jet cutters can only reach 700 Mpa - and that limit is going to apply to your car tank filler." But I showed you a diagram that is suppossed to act as a funnel. Does it not work this way? If not, why not? The key insight here is that you don't care about the internal pressure of the 1000 Mpa or 800 Mpa or whatever, you just need it output over a large surface. So although you can store it at such an internal pressure, you can get it out over a large surface, gradually. What would happen if, for example, my diagram had a sturdy pump balloon over it (like a pump) with a one-way valve letting it draw air in from the the outside, you squeezed it over a large area, then you let it draw air again. It would look like this: http://i.imgur.com/StAED.png - single arrows are pressure, double arrows are movement. At the left of the three, the pump is neutral. To get to the middle, squeeze the pump: it now expels over a LARGE surface area into the snail. Once you've finished squeezing it, you release. The one-way valve gets snapped shut and you get to the third of the three pictures in which air streams back into it as it expands due to its rubbery shape. (Or it can be pulled open again mechanically.) What do you think?
For hydrogen this works and is near production. See [17]. However, it depends on specific properties of the nanotube interacting with hydrogen to stabilize it - it's not just a tiny pressure tank, it actually sucks up the hydrogen, more or less. Wnt (talk) 19:46, 9 January 2013 (UTC)[reply]
Oh, yeah - FYI: [18] says that the diameter of the carbon nanotube cable needed to support a space elevator would need to vary between one and 16 centimeters...not "a few molecules wide" as you assert. Indeed one of the most cited scholarly papers on the subject ([19]) concludes with "It is the author’s opinion that the cable, if realized as designed today, will break.". It's strongly likely that carbon nanotubes are incapable of supporting such a structure at any diameter. SteveBaker (talk) 14:44, 10 January 2013 (UTC)[reply]
Right, which is why in part this wasn't really a question about carbon nanotubes as a magic weight-free substance that obeys physics but can store any pressure. I was interested in aspects such as the heat, and the fact that the result would still have to weigh something, and also we have just found out that pumping into it at arbitrary pressure might not be that easy or fun. 91.120.48.242 (talk) 16:05, 10 January 2013 (UTC)[reply]
I still like the thought experiment where you assume perfectly strong materials and an infinitely powerful pump. After all, the original question did specify a container of "infinite tensile strength." Let's assume that you compress your [whatever - it doesn't matter what you start with] down to a tiny, tiny sphere of pure neutronium. Then you let it expand a bit at a time to power your vehicle. And you use that handy infinite-strength material to stop it from falling through the bottom of your car and heading for the earth's core.
Neutronium has some advantages as a fuel. Because it contains no protons, it is not radioactive. Because it has no electrons, it is totally chemically inert. I am not even going to guess at the hardness or tensile strength. And when it expands you can, in theory, have it expand into any element. I want my car to create gold bars as the exhaust.
The main disadvantage is that Neutronium is that it is incredibly dense: 4*10^17 kg/m^3 (four times ten to seventeenth power kilograms per cubic meter) -- about a million million times heavier than lead. So you need your chunk of neutronium to be very tiny, otherwise your vehicle will weigh many tons. And I am not sure whether I want to be on the same planet if it ever expands all at once. --Guy Macon (talk) 21:31, 10 January 2013 (UTC)[reply]
I guess people are either taking my "hypothetical" version too far or not far enough. Not far enough when they get bent out of shape about how many PSI we can pump or the PSI that our current materials support: I asked you to assume we could pump, and assume that a weightless material supports any psi. However, they take it too far when they then think that we can get to a neutron star, since I expressly said that my experiment should have NO other special properties: it doesn't insulate, it doesn't make your material weightless, it doesn't prevent the exhaust, etc etc. So, I would think that at the point where I place my mental experiment, where hte ONLY three things we elide are: 1) the pump mechanics; assume we can pump at any PSI into the container; 2) the container itself's weight, 3) the container itself's ability to ohold pressure, which are assumed to be infinite, 0, and infinite respectively. This assumption still leaves you having to deal with the weight of the gas, as well as with any phase transitions as pressure comes out of the pump, and with the temperature problems. Under these circumstances, how much "weight" could we ACTUALLY (asssuming 3 magic assumptions) pump into a car? Surely no more than a few tons. So, how much energy does a few tons (say, ten tons) of air represent when compressed into a gas tank mobile size. What PSI does that get us. How much do we have to deal with the thermal problem? 91.120.48.242 (talk) 07:42, 11 January 2013 (UTC)[reply]
What is the difference between anode rays and canal rays ?
Last paragraph of article Anode ray says As these perforations were named as canal so these rays are called canal rays. These are not the anode rays as these were not originated from the anode. The article doesn't clearly describes how these two rays are different. Please help ! Want to be Einstein (talk) 15:03, 9 January 2013 (UTC)[reply]
This terminology (and this technology) is not in common use in this century. So, it's really a matter of historical interest to quibble over the finer points of this terminology. Our article already links to a reprint of a 1913 article, Rays of positive electricity, published by J. J. Thomson; you can rest assured that he used his terminology consistently. As with all scientific jargon, different scientists have used different variations; but as of today (2013), not many people at all are actively publishing descriptions of these types of devices using that terminology. Most books and papers today will talk about charged ion beams or electron beams, and will talk about the positive and negative particles, or device terminals, (rather than the more confusing "anode" and "cathode" terminology). You'll still hear the term "Cathode Ray Tube" in common use, because those devices had such an important historical impact; but you won't be hearing about CRTs for very much longer, as almost every single use for vacuum-tubes - from display monitors to klystron microwave amplifiers to Bremsstrahlung x-ray sources - have all been replaced by better semiconductor or solid-state alternatives. Nimur (talk) 19:34, 9 January 2013 (UTC)[reply]
Every single use, Nimur? Not for a good while yet. To generate microwaves for cooking, at continuous power levels of several hundred watts, nothing beats a cavity magnetron, a type of cathode ray tube that is nothing more than a heated cathode surrounded by a shaped anode. Want to know what is the cheapest, most stable, easiest way to accurately (say 3- to 4-digit accuracy) measure voltages 30 kV and up? A triode valve (preferably a tungsten filament valve) - a type of cathode ray tube! You use the anode as the input, earth the grid, and vary the cathode voltage (typically 10 to 20 V or so) to get a specific cathode current (microamps or less), virtually none of which flows in the grid. The relationship of anode voltage to cathode voltage at a specific current is precisely linear within a good working range, dependent only on the tube physical geometry. The relationship to current is well understood (the "three halves power rule"). At lower voltages, or high voltages at lower accuracy, voltmeters normally use multiplier resistors. However, getting accurate stable resistors for 20 kV and up is not trivial - usually 2 digit accuracy is as good as you can get. There's also the old gold leaf electroscope, but they have woefull accuracy and are not linear. There's other niche applications for vacuum tubes/cathode ray tubes too. Keit 121.215.151.39 (talk) 23:44, 9 January 2013 (UTC)[reply]
Valid points. High-power solid-state devices are encroaching, but have not totally replaced tubes in some applications. By 2025, I suspect you'll even see microwave ovens using switch-mode IGBTs instead of cavity resonators. And I am not alone in this speculation: Power Electronics magazine published a technical article on 100 kW solid-state (IGBT) converters - so there's hardly any power- or frequency- regime that is "off-limits" for semiconductors. Pick up your favorite microwave or RF newsletter, and you'll see higher- and higher-power RF implemented in silicon. You are correct; the highest power systems haven't made the switch, yet. But it's a matter of time. Solid-state power is cheaper, safer, easier, better, more efficient, ... all the reasons that all other industry applications have switched to semiconductors. Nimur (talk) 00:09, 10 January 2013 (UTC)[reply]
You are certainly correct in saying vacuum tube technology is obsolete for most applications - that is very obvious. However niche applications for tubes continue. IGBT's are inherently low frequency devices and will not replace magnetrons. If you read the article about switch mode power conversion you linked to, you'll see they think 50 kHz is a good achievement. The triode valve method of measuring extra high voltages works well for short (microsecond) pulses too - nothing else does. Keit 124.178.60.57 (talk) 00:21, 10 January 2013 (UTC)[reply]
(Edit Conflict)
(Note: every technical explanation on the Internet must by law contain at least one glaring error that makes the writer look like an idiot...)
Start with a bunch of atoms in the form of a gas.
Cosmic rays and natural radioactivity knock electrons off, making (a few) ions - atoms that are missing an electron.
Apply a high voltage across the anode and cathode (typically made of metal)
High voltage accelerates ions toward the negative cathode.
Ions hit atoms in gas.
This knocks electrons off of atoms, making many more ions - a chain reaction
High voltage accelerates ions toward the negative cathode.
So we have ions traveling from the anode to the cathode - Anode rays.
Meanwhile the electrons travel from the cathode to the anode - Cathode rays.
(You can also get electrons from a heated cathode, but that's another story.)
In 1886 when Eugen Goldstein was first figuring this out, it was hard to look at the anode rays and cathode rays going past each other both ways and figure out which was which.
Goldstein put small perforations (canals) in the cathode.
Some of the ions in the anode rays passed though the canals.
Now he had a ray that was just the ions from the anode ray, with no electrons from the cathode ray to confuse the issue.
He called these rays that left the cathode in the opposite direction as the cathode rays (but only if the cathode had "canals") "Canal Rays" and the name stuck.
And yes, our article explains this poorly. Canal rays only appear to originate in the "canals". Then again, few engineers talk about "rays" or "cathodes" anymore. We talks about Electrons, Ions, negative terminals and positive terminals. Still, you see the old terms in a lot of the early papers from the scientists who discovered this stuff. --Guy Macon (talk) 19:53, 9 January 2013 (UTC)[reply]
"(Note: every technical explanation on the Internet must by law contain at least one glaring error that makes the writer look like an idiot...)" - the entire Reference desk system depends on this fact to keep us all interested! SteveBaker (talk) 20:16, 9 January 2013 (UTC)[reply]
Buoyant force
Suppose an object with flat base placed in a container containing water and container also has flat base. The object has rectangular shape and its density is lower than water. The object is submerged (by hand) into water in such a way that its base touches the base of the container. In that situation, there is almost no water below the object and also there is whole water of the container above object and the weight of this water column lies on the object. When the hand submerging the object is removed from water, the object comes on the surface of water as it has lower density than water. The question is:Why does object come on the surface even when there is no water below object to push it up and also the object is forced down by the weight of water column above it ? Does buoyant force depend on the amount of water present below an object ? I tried my best to explain where I got stuck, thank you for answering my question. Sunny Singh (DAV) (talk) 16:48, 9 January 2013 (UTC)[reply]
The pressure of the water is proportional to depth, and any air trapped below the object will exert the appropriate pressure under the object for that depth (being greater than the pressure on the top of the object at a lower depth). If you succeed in producing a seal round the edges of the base, and allow a tiny amount of flexibility so that the trapped air can expand, then the pressure under the object may well become lower than that on the top, so the object will not rise but "stick" to the bottom of the container. I think the same could happen to a very small quantity of water if inrush of water below the object is prevented. Dbfirs17:09, 9 January 2013 (UTC)[reply]
There is always going to be some water under the flat-bottomed object - you can't get a perfect contact between those two objects. But just do the thought-experiment of removing the water and just pushing the two objects together in air. If there was a perfect seal between the two objects, they'd be held together by the air pressure just like a suction cup on a sheet of glass! The deal in water is just the same. But if there is *any* gap, then water will intrude and because pressure in a liquid or gas exerts a force equally in all directions - there is nothing to prevent the object from floating away. SteveBaker (talk) 17:54, 9 January 2013 (UTC)[reply]
Aquaplaning or hydroplaning might be relevant. A very very tiny amount of water - just a few drops! - can be put into circumstances such that it has a very high dynamic pressure. In those cases, those few drops of water are sustaining the weight of an entire object above them - sometimes resulting in pressures equivalent to many thousands of PSI! That's enough to lift the entire weight of a heavy object - like a truck or a car or a four-hundred-ton cargo aircraft. This is a problem worthy of an entire NASA facility, the Aircraft Landing Dynamics Facility at NASA Langley. Here are some fun videos of this research: NASA Research on Hydroplaning. All this trouble comes from the fact that water is almost totally incompressible. Just a few drops of water will still occupy the same volume even if they are put under the crushing weight of thousands of atmospheres of pressure. Almost no water, if suitably constrained by a container, is therefore able to buoyantly lift a very very heavy object. Nimur (talk) 19:08, 9 January 2013 (UTC)[reply]
The same is, of course, true of the bottom of the very very heavy object. Ultimately there is only one layer of atoms at the bottom of anything, yet they hold it up. I think that SteveBaker's thought experiment works very well. Consider an object "stuck" to the bottom of a pool because there is a suction cup or other "vacuum" under it. What makes that a vacuum is that it is lower pressure relative to the water at the very bottom of the pool; in other words, we normally expect that pressure to propagate through perfectly. I suppose what amazes most is that physics is so good at "doing the math" - in other words, that if you have a narrow tube filled with atoms of water constantly moving about, that somehow the water at the near end and at the far end manage to come into such perfect agreement about what the pressure really is. The same amazement strikes people with other events, such as the ability to do DNA hybridization of a primer with a specific sequence out of an entire genome - as we see in that case, the computational power, though extraordinary, does have limits. Still, it is pretty amazing when you consider that the molecules doing the "math" by smashing together are moving only somewhere on the order of the speed of sound (I'm not entirely sure about the relation of this to the thermal speed according to the Boltzmann constant). Wnt (talk) 19:43, 9 January 2013 (UTC)[reply]
The point is that although they are only moving at the speed of sound, they are moving an incredibly short distance until they hit something and transfer the information. So the number of collisions per second is an ungodly high number - and that's how come this "calculation" happens so fast. SteveBaker (talk) 20:13, 9 January 2013 (UTC)[reply]
A related concept is Choked flow in a hydraulic or pneumatic system, where opening up a valve further downsteam has no effect on flow upsteam because there is a section of pipe with supersonic flow between them. It's the pneumatic/hydraulic equivelant of the speed of light; no information can travel faster than the speed of sound in the gas/liquid, so the upstream system doesn't "know" you opened the valve downstream. --Guy Macon (talk) 20:16, 9 January 2013 (UTC)[reply]
Depth won't matter, in fact the deeper it is, the less stable it is.. If the object maintains it's volume and the density is less than water, it will float. Extreme depth submarines used gasoline (incompressible fluid that is less dense than water). There is no "floating force", rather gravity pulls on the denser water harder than on the object. The system is in unstable equilibrium with the less dense object on the bottom and will revert to a lower energy state of stable equilibrium. Think of a rod pinned in the middle with a heavy ball at one end and a lighter ball at the the other. Trying to make the lighter ball stay at the bottom is difficult because the slightest perturbation will cause it to swing to a lower energy state. The same is true for your block in a water column. It is statically in equilibrium, but any perturbation will cause the system to revert to the lowest energy state which is the denser water beneath the floating block. It is directly analogous to mechanical equilibrium. There is a static solution where the block can remain at the bottom, it's just not a stable solution and the system will revert to the lowest energy state --DHeyward (talk) 09:29, 10 January 2013 (UTC)[reply]
I thought that Sunny Singh was asking about forces. The "static equilibrium" of your claim will occur only when water is prevented from flowing underneath. This is different from your example of unstable equilibrium. I see why you made the comparison, but I don't think it helps to answer the question (unless I misunderstood the question, of course). Dbfirs21:02, 10 January 2013 (UTC)[reply]
Butterfly flight
this is totally from left field, based on a single observation: a cabbagemoth butterfly was flying right to left - a stiff breeze arose, blowing in the opposite direction - but the butterfly continued unperturbed, whereas one would expect it to be blown away.
Possibly the air current wasn't wide enough to reach both me and the butterfly - but possibly it was. I thought back, and couldn't think of a time when I'd seen a butterfly blown off course. Has anyone here? Have they some as-yet-un-understood mechanism for beating the wind?
I think they just stay grounded during heavy winds. As you said, the wind current you observed must not have reached the butterfly. StuRat (talk) 23:09, 9 January 2013 (UTC)[reply]
Thanks, StuRat, you're most likely right - but let's wait and see if others have made the same observation and we can end up naming a whole new principle after me. Adambrowne666 (talk) 02:37, 10 January 2013 (UTC)[reply]
I live in a suburb in the hills near the edge of a state forest and we get lots of butterflies, I saw easily more then a dozen just the other day while working outside. Nothing about their flight made me think they were not being affected by the breeze, but I always thought butterflies weren't very gracefull fliers even when it's calm. I must admit i wasn't specifically looking for that. I'll make note and watch some butterfiles more closely next time. Vespine (talk) 02:54, 10 January 2013 (UTC)[reply]
Thanks, Vespine; maybe they appear to be poor fliers, but are in fact very good. And surely they can't always know when there's about to be a stiff breeze and ground themselves. Let us know if you notice the same thing I did. Adambrowne666 (talk) 12:03, 10 January 2013 (UTC)[reply]
January 10
Hand grenade, part 2
What are the lethal radius, stun radius and injury radius for a German stick grenade? I want to know if that pesky German machine-gunner will end up killed outright or not. Thanks! (Oh, BTW, while we're at it, are these radiuses significantly affected if the explosion takes place inside a concrete pillbox?) 24.23.196.85 (talk) 00:25, 10 January 2013 (UTC)[reply]
As for the pillbox, it will make damage must worse inside, both from overpressure and fragmentation (with pieces ricocheting off the walls), while those outside should be relatively safe, unless standing right by an opening. StuRat (talk) 00:40, 10 January 2013 (UTC)[reply]
So, how much damage can the enemy gunner expect to take (A) 8 feet from the blast (if he stays at his post), or (B) 15-20 feet from the blast (if he leaves his machine gun and retreats deeper into the pillbox)? Assume that in both cases, the blast happens inside the pillbox. 24.23.196.85 (talk) 07:06, 10 January 2013 (UTC)[reply]
A "pillbox"
(I am rapidly becoming an expert on stick grenades thanks to User:24.23.196.85's questions!)...The answer will depend to a huge degree on whether the year is before 1942 - when the grenade had a thin metal shell around the explosive - or after 1942 when the person who threw it could choose to place a "Splitterring" over the head of the grenade (or not). The Splitterring was a special cylindrical steel shell that wrapped around the grenade to increase the amount of fragmentation - at the cost of decreased blast radius. If the year is after 1942 and the person who threw the grenade had a splittering about his person and had appropriate training in when to use it - then they would certainly have used it against the pillbox.
There would be two main causes of injury - overpressure from the explosion and injury from the flying fragments. There might also be burn injuries. Inside a very tightly enclosed pillbox, the overpressure would be much higher than out in the open - and the fragments produced by the grenade would ricochet off of the hard concrete walls to produce a much deadlier effect...much more so if the splitterring was used.
The "effective blast radius" of the later model grenades (7oz of TNT) was 16 yards. The earlier models only had 4oz of explosive. Even if reduced by a splitterring - that would be ample to produce lethal overpressure in the confines of a pillbox. The victim might avoid the fragmentation effects if he could hide around a corner or in another chamber - but pillbox bunkers such as the one in the photo are typically nothing more than a hexagonal concrete box with some holes to shoot out of and a door at the back to get into and out of - so that's unlikely.
Best guess is that he's dead if he's 8 feet from the blast...and not many pillboxes are large enough to get 15 to 20 feet away...they really aren't that big. His only real chance is if this is a really large pillbox with an internal concrete wall and the thrower used a splitterring on a early Mk 24 grenade (with only 4oz of TNT) - which together reduced the blast radius by enough to keep the over-pressure survivable - whilst producing fragmentation that the occupant could avoid by getting into the adjacent room. But moving 15 to 20 feet away - and into another room - in the very few seconds available seems extremely unlikely! Hence, IMHO, he's dead no matter what.
The pillbox in your picture seems to be Czech but bears a striking similarity to the rather amateurish British Type 24 built in a panic the summer of 1940. The Germans. who liked to think of themselves as the masters of mobile warfare, were actually rather fond of hiding in the biggest and most elaborate concrete structures that the Organisation Todt could devise. Alansplodge (talk) 20:58, 10 January 2013 (UTC)[reply]
Thanks for the info, everyone! Just FYI, the pillbox I have in mind is of the half-moon type with access by bent entrance, and the gunner in question is manning the gun that is guarding the entrance to the pillbox; as for the grenade, it's a 1944 model (the scene takes place during the Battle of St.-Lo) without a Splitterring (the good guys here are Maquis, who generally didn't have access to such things). So the bottom line is, they'll find the gunner sprawling on the floor and as dead as a depth charge -- just like I thought. 24.23.196.85 (talk) 23:47, 10 January 2013 (UTC)[reply]
Oxygen, fire, and inorganic
Why do CO and CO2 is classified as inorganic even when they have carbon atom in their molecule ?
What make oxygen a supporter of fire and carbon dioxide a detractor (non-supporter) of fire ?
CO and CO2 are not of biological origin, though I'm not particularly good with the definition either.
Oxygen is a reactant in the combustion reaction we call fire. In most rate equations I've seen, fire's rate is greatly increased by the concentration of oxygen. This makes sense because the probability that oxygen molecules collide with fuel at sufficient speeds to cause a reaction is greatly increased. Likewise, carbon dioxide is an inhibitor which can act by decreasing this probability.
The fire article says that the flame is the visible part of the fire. There also exist non-visible parts of a fire, like the embers. Again I'm no expert with this definition.--Jasper Deng(talk)06:25, 10 January 2013 (UTC)[reply]
The Wikipedia article Organic compound states it rather eloquently "The distinction between "organic" and "inorganic" carbon compounds, while "useful in organizing the vast subject of chemistry... is somewhat arbitrary". the ultimate answer is that there is not a good, sound reason for it besides the fact that its a historical artifact that has been dragged through the classification system. The article has some background of how they came to be excluded, but ultimately CO, CO2 and the Carbonates are not considered organic just because. That's the best we can say, really. Sorry.
Oxygen atoms form strong bonds with other atoms. The stronger the bond formed, the more energy released in the process of forming it. So, just about any reaction that results in atoms that were formerly bonded to other atoms to bond to oxygen results in a large release of energy. The converse is true: to break bonds to oxygen, or to replace bonds to oxygen with bonds to other atoms, would require a huge input of energy. Thus, reacting a hydrocarbon with oxygen gas (forming water and CO2) releases a bunch of energy, because of the formation of the stronger H-O and C=O bonds (compared to the original C-H and O=O bonds), and would require the same input of energy to reverse. Now, it isn't strictly true that nothing burns in CO2; you just need to find a way to make a compound that is even more stable than CO2. See This reaction of magnesium in carbon dioxide, a common demonstration.
Flame is the glowing gases in a fire. The fire is the entire reaction itself, including the solids and liquids and smoke and all together. It may be better to think of fire as the process and flame as the glowing gas. --Jayron3206:45, 10 January 2013 (UTC)[reply]
The synthesis of urea (and other organic substances) from inorganic compounds refuted the idea that organic matter possessed a vital force
As noted in the article organic compound there isn't universal agreement on which molecules are "organic". Some textbooks, including one I had years ago, consider all carbon based molecules to be "organic", including CO2 and CO. I think it is more common to simply define some small carbon-based molecules as inorganic, but the set of molecules to exclude is largely historical and the result of drawing fairly arbitrary lines. For example, saying that "organic" molecules must have C-H or C-C bonds in them, while excluding molecules with only C-O or C-N bonds, even though the latter are also widely present in biology. Dragons flight (talk) 11:36, 10 January 2013 (UTC)[reply]
The historical origin of the term is a common theme in books on the history of science. While many life forms do produce CO2, oxygen-carbon aerobic respiration is a late development so far as the history of evolution. That CO2 is found in nature without being produced by living organisms, unlike compounds such as urea provides the origin of the term. Originally, organic compounds were those that were only found in or produced by living organisms. Eventually it was discovered that those compounds almost universally contained carbon. The synthesis of urea in the lab was highly significant in the history of science, since it showed that no special vital force unique only to living beings as had been supposed was necessary for the creation of these substances.
The term has generally evolved to refer to hydrocarbons and their more or less complex derivatives in general and of whatever origin, given the hypothesis of a vital force was found false and unuseful. Whether one prefers the carbon-based or hydrocarbon-based definition is simply a matter of convenience. There are a relatively (!) small number of simple carbon compounds not containing any hydrogen, and their behavior is different enough from typical hydrocarbon derivatives that excluding them from consideration may be convenient, say, for biologists rather than chemists. μηδείς (talk) 20:32, 10 January 2013 (UTC)[reply]
Well, except that isn't strictly true. Carbon dioxide participates in reactions not unlike analogous "proper" organic molecules, for example it undergoes Grignard reactions, a common synthesis of carboxyls: R-MgBr + CO2, acid workup --> RCOOH[20]) This is exactly analogous to the Grignard reaction with an aldehyde: R-MgBr + R'CHO, acid workup --> R-CHOH-R'[21]. --Jayron3220:40, 10 January 2013 (UTC)[reply]
Are you talkin' to me? Hehe. I am not sure what you are denying the truth of, Jayron, something I said or someone else said. μηδείς (talk) 20:43, 10 January 2013 (UTC)[reply]
You stated "simple carbon compounds not containing any hydrogen, and their behavior is different enough from typical hydrocarbon derivatives...," which isn't really that true. In many ways, CO2, one of the "simple carbon compounds not containing any hydrogen" does not significantly deviate from organic molecules in terms of its reactivity or behavior. Sure, CO2 doesn't behave exactly like any other molecule, but only insofar as no two molecules behave exactly the same anyways, and CO2s chemical properties behave pretty much as would be expected as if it were treated like an organic molecule. The Grignard example I gave above is representative, not exhaustive, of the way in which CO2 works in organic chemistry. --Jayron3220:50, 10 January 2013 (UTC)[reply]
Oh. Well, I am not myself saying that CO2 should or should not be excluded--it is a matter of convenience. I am quite aware that CO2 is a reagent in a lot of organic chemical syntheses. But the properties of CO2 are very different from hydrocarbons. The basic point is that historically, the term was used in a way that excluded CO2 for biological reasons, which is the strict answer to the OP's question. Nowadays chemists use the term synonymously with carbon chemistry. That doesn't befront me. μηδείς (talk) 21:00, 10 January 2013 (UTC)[reply]
Why is the ampere and not the coulomb an SI fundamental unit?
As a fourth year high school student, I'm currently studying high school physics. I know that the SI unit of charge is the coulomb while the SI unit of electric current is the ampere. They can be defined by each other (1 C = 1 As while 1 A = 1 C/s). However, it is the charge of an atom's protons and electrons which allow electric currents to occur in the first place. By this logic, shouldn't it be the coulomb and not the ampere that should be an SI fundamental unit, since the coulomb measures charges, and electric currents are just a manifestation of charges? Is this because of historical reasons, convenience or calculation reasons? Narutolovehinata5tccsdnew11:06, 10 January 2013 (UTC)[reply]
Yes, it is mainly for historic reasons. It is also easier in practice to measure a current than to measure a quantity of stationary charges. In calculations however, it doesn't really matter which is the fundamental unit. Oh, and I think you made a small mistake: (1 C = 1 As while 1 A = 1 C/s) - Lindert (talk) 11:24, 10 January 2013 (UTC)[reply]
As discussed in new SI definitions, there is a current proposal to define the electric charge as an exact constant with the effect that a Coulomb would represent an exact number of charges. Even so, the Ampere would still be considered the "base" SI unit for historical reasons. Dragons flight (talk) 11:41, 10 January 2013 (UTC)[reply]
Narutolovehinata5 has asked an excellent question. It demonstrates clear thinking about physics and units of measurement. Well done! Dolphin(t)11:47, 10 January 2013 (UTC)[reply]
Last time I looked, the elementary charge, symbol e, value 1.602 176 565 x 10-19 Colomb, IS a fundamental physical constant. What's fundamental and what is derived gets changed in the SI system from time to time as knowlege and measurement capability improves. Perhaps you are using an out of date textbook, or your texbook has regurgitated out of date information from another textbook. That happens very frequently in high school texts (and college texts too for that matter). It's importnat too, to understand the difference between standards and fundamental constants. While the ampere can be calculated from fundamental units of charge and time, the calibration of instruments will proceed from a primary standard apparatus held in Standards labs that provide a standard ampere. A known ampere can then be used to calibrate instruments that measure other things. See http://en.wikipedia.org/wiki/Elementary_charge Ratbone 121.215.62.231 (talk) 12:05, 10 January 2013 (UTC)[reply]
Hmmmm... The Wikipedia article I linked says in its second sentence "This elementary charge is a fundamental physical constant." It appears we have a conflict between two articles. I notice that the SI Base units article is based on the 2005 SI standard (Ref 1 in the article). The change was proposed back then. Was it not changed in 2007? Ratbone 124.178.177.177 (talk) 13:14, 10 January 2013 (UTC)[reply]
The 2005 (and later) proposals do not change the list of units defined as "base units" by the SI system, even though it would change how the Ampere is calibrated experimentally. Dragons flight (talk) 13:21, 10 January 2013 (UTC)[reply]
I don't understand why people are discussing the elementary charge, because it's irrelevant to the question. The ampere is a base unit because current is easily measurable and very commonplace in electronics, whereas charge is not. That's as much a historical reason as a current convenience reason.
Literally everything about the SI system--from its design, to its choice of units, to the continually-changing definitions of those units--are for the convenience of us humans. If we can't easily use a unit or reproduce its value based on its definition, it's useless, because the Universe couldn't care less about what humans use to describe it. --140.180.240.178 (talk) 05:00, 11 January 2013 (UTC)[reply]
Precor treadmill's interval settings
There are only Precor treadmills in my gym. I started my interval training this week. I plan to do high-intensity interval training maybe twice a week.
I noticed that Precor's presets are 2, 4, or 6 mins of work and 2 mins of rest. Some more advanced models are programmable but the model in my gym seems to be fixed. Very few people bothered to tweak the settings.
However, most articles that I have read about HIIT said that the intervals shall be much shorter in order to be very very intense. Such as Wikipedia's HIIT article:
The original protocol set a 2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking.
Many Android interval apps also have similarly burst settings.
Certainly I can do two minutes of sprinting. But I can run much faster if the interval is set to 30 seconds. Are the two minutes intervals compromise the HIIT? -- Toytoy (talk) 12:48, 10 January 2013 (UTC)[reply]
It's pretty dangerous to use a treadmill at sprinting pace, and especially to bring it up to sprinting pace very rapidly, or down from sprinting pace. If you want to follow such a protocol, I wouldn't do it with a treadmill. Looie496 (talk) 18:18, 10 January 2013 (UTC)[reply]
Agreed, you'd need a special much larger treadmill, to make falling off less likely, and nice soft surfaces on all the sides, in case you still managed to fall off at full speed. StuRat (talk) 04:16, 11 January 2013 (UTC)[reply]
If you can't keep up with the pace, running on the treadmill can be very dangerous indeed.
I wonder why the Precor 954i does not have some sort of alarm that flashes red light and makes a little noise to let you know it's going to get faster.
If danger is a reason why treadmills do not provide HIIT options, you can still set the treadmill to switch between 12 mph (the maximum speed) and 0.5 mph every two minutes. This can still be very dangerous. I use inclination change (0 to 5%) to get me notified. The Precor model allows up to 15% inclination. However, I think the gym disabled anything steeper than 5%.
OK, maybe next time I'll do HIIT on a stationary bike or an elliptical machine. They are not supposed to kill you. Otherwise I'll do HIIT when I am jogging (if the weather becomes a little better). I'll wear a heartbeat monitor just in case. -- Toytoy (talk) 16:04, 11 January 2013 (UTC)[reply]
A 3,500 lb specimen of the Ocean Sunfish, or Mola Mola
This fish is huge (up to 5,000 lbs) and ungainly, and supposedly non-toxic. It seems so much like floating meat it reminds me of this animal. Has anybody got any information on how it defends itself? Thanks. μηδείς (talk) 20:06, 10 January 2013 (UTC)[reply]
Yes, the point of it seeming to be they don't have any defenses. Kind of one of the Creator's cruel jokes, like the animal in the video I linked to. I realize the small ones have spikes. What I am curious of is if the large ones taste bad (in Asia they're a delicacy) or something else. Being big enough only to be a slow-moving shark and aquatic-mammal appetizer doesn't exactly strike me as a "defense". μηδείς (talk) 20:50, 10 January 2013 (UTC)[reply]
Animals don't need "defenses". To persist as a population, they just need to reproduce more than they die (or about equally on average). Our article says that Mola Mola females "produce more eggs than any other known vertebrate." Sure, a lot get eaten, but some don't (see r/K selection). Also, fecund females can produce eggs over several years. This could potentially form a storage effect that buffers the population against bad bouts of predation, but that's approaching WP:OR.
We don't have an article on it, but the main thing governing species persistence is the long-term, low-density growth rate, which quantifies how strongly a population can "bounce back" after some perturbation to low density. You can search that term on google scholar to find several interesting articles, though they tend to be theoretical. From a more applied perspective, you may be interested in Population_viability_analysis. And really, their adult size does surely reduce their predation, compared to smaller fishes. Finally, you may enjoy these course notes on population growth [22]. SemanticMantis (talk) 21:55, 10 January 2013 (UTC)[reply]
You know, you are absolutely right, because although I noted the very high value of r, I was still thinking of them as a K-selected species because of their huge adult size. (It still amazes me that any of them live past the spiky fry stage.) And even though they are obviously r-selected, they may still have undesirable traits such as their skin, which is compared to color-changing mucus covered sandpaper. Their similarity to sea turtles, which also graze jelly-fish, is also interesting. μηδείς (talk) 23:26, 10 January 2013 (UTC)[reply]
It still amazes me that any of them live past the spiky fry stage ... Does living with the jellyfish help them survive? I mean if you eat jellyfish, you probably spend much of you time living with them. Jellyfish around them may prevent them from being eaten by sharks. -- Toytoy (talk) 15:40, 11 January 2013 (UTC)[reply]
The more I think about it, the greater it seems that as grazers of the ever-abundant jellyfish, sea turtles and the Mola Mola have converged on a r-selected niche with bodies adapted for low-energy stability in the water column. Is there any mention of such a niche, and would there be any mesozoic creatures, perhaps reptiles or cephalopods that fit it? Thanks. μηδείς (talk) 01:38, 11 January 2013 (UTC)[reply]
Along those lines, but the elasmosaurs are usually portrayed as darting after fish and the pliosaurs are more like carnivorous whales. I'll have to get a good illustrated book on the marine reptiles from the library, anybody have suggestions? μηδείς (talk) 03:55, 11 January 2013 (UTC)[reply]
If I understand your question correctly, the nautilus seems to fit all your criteria: lays lots of eggs, neutrally buoyant, around since before the Mesozoic, and a cephalopod.--Wikimedes (talk) 10:51, 11 January 2013 (UTC)[reply]
Last grenade question, I promise
If a grenade detonates inside a concrete pillbox, is it plausible for the blast wave to reflect off a wall and travel around a corner to hurt/stun or even kill an occupant despite him not having a direct line of sight to the point of the explosion? (No, I haven't changed my mind about bouncing the thing off the walls and around the corner -- I'm pretty sure that can be done with no more than two bounces -- but if it lands short, would it still be capable of hurting or even killing the gunner?) 24.23.196.85 (talk) 04:35, 11 January 2013 (UTC)[reply]
I'd say it's even more effective than relying on fragments to ricochet at the angle needed to hit the victim. Concrete walls will probably be as close to perfect mirrors WRT sound as they come on a WWII battlefield. With fragments, you need to get lucky. With pressure shock, it's just cold hard mathematics (followed by quite messy forensics). I'd really hate to get caught in the focus of some concave wall... - ¡Ouch! (hurt me / more pain) 07:20, 11 January 2013 (UTC)[reply]
The next one to ask a grenade question will have it thrown back at them! Just kidding.
Think of the pressure wave as if it were sound (which, it technically is!) - sound would bounce ("echo") from a concrete wall very well - and so will the blast wave. Sound has very long wavelengths and will also refract through doorways and outwards as it leaves your short corridor. SteveBaker (talk) 07:30, 11 January 2013 (UTC)[reply]
Concrete walls are pretty good acoustic mirrors, sure - but explosive shock waves are often supersonic - hence shock wave - so intuition may not lead to the correct conclusion. In shock, pressure waves do not superimpose in a straightforward way. So, while I agree with Steve, the pressure-front will expand, and will reflect; but we need to tread carefully if we use any simplifying assumptions about exactly where the reflections go, or how strong they will be. For example, an explosive front doesn't propagate at the sound speed. And the intensity doesn't fall off with the square of the distance. (Both are pretty good equations for modeling sound waves). There's an incredibly huge volume of published research - entire text-books - on the subject. The interested readers can start browsing articles and links from, e.g., detonation; deflagration to detonation transition.
Now, as far as a reliable source specific to warfare, I recently read through most of 'Sharpening the Combat Edge', "THE USE OF ANALYSIS TO REINFORCE MILITARY JUDGMENT", written by the commander of the 9th Infantry Division in southern Vietnam in 1968 and 1969. This takes a totally different, but equally-analytic approach: instead of trying to derive blast-radius from first principles of physics, the authors statistically studied the actual effects of the explosives they encountered during combat: and then performed fact-based and statistics-based analysis to determine things like blast-radius. There's a chapter on mines and booby-traps: " approximately three-fourths of all devices were trip-wires attached to a grenade..." As the commander of the infantry division notes, it's important to know this simple fact: how far away from a grenade is "safe"? "The advantages of an analytical approach are demonstrated by setting optimum distances between men based on simple field tests with the most frequent types of traps. If this distance was maintained, multiple casualties were infrequent. ...The 25th Division elaborated upon this type of analysis by placing the data on their computer, thus giving them the capability to present and study the problem with minimum clerical effort." As a computer-enthusiast, I am absolutely astonished that a combat infantry division, staffed primarily by conscripted riflemen, was operating a computer in the field ... in Viet Nam ... in 1967. Forward-thinking! Innovation manifests itself in the most unexpected places... Nimur (talk) 15:49, 11 January 2013 (UTC)[reply]
Another way to look at the lethality is that 7oz of TNT produces about 0.6 MJoule of explosive energy and about 3MJoules of heat. The resulting shockwave leaves the surface of the explosive at about 15,000 mph. In a very enclosed space (and a pillbox is about the most enclosed space imaginable!) with efficient reflectors (reinforced concrete!) - where will all of that energy end up? An easily deformable/compressible human body will end up collecting a good proportion of it one way or another. SteveBaker (talk) 16:51, 11 January 2013 (UTC)[reply]
Death
When do children know that humans are mortal? When do they know that they will eventually die, and never live again? I've found two unreliable websites that claim children begin to appreciate the finality of death when they're around 10 years old. I'm young enough to remember some of my childhood, and that seems extremely implausible--I remember thinking about murder and suicide around that age, and definitely didn't believe either was temporary. --140.180.240.178 (talk) 04:36, 11 January 2013 (UTC)[reply]
It will depend greatly on culture, the attitude of parents, and the child's environment. I grew up on a farm and definitely understood death and that life doesn't go forever as far back as I can remember particular animals dying, at about 5 years of age. Children who have fragile pets such ginea pigs will certainly understand it. What might be harder to figure out is at what age children assign a level of distress to people, mammals and birds they know dying, as distinct from merely accepting that the dead person/mammal/bird/etc has had life extinguished and won't be back.
In management training, I was taught that there are 5 distinct stages of grief that people go though whn receiving bad news, always in the same order. Depending on which book you read, they are something like denial, anger, bargaining, acceptance, conversion. See http://en.wikipedia.org/wiki/Five_stages_of_grief. Some people pass thru one or more stages almost immediately - some people stay in one stage for a long time - even months or years. It may be of greater value to ascertain how children at various ages go thru the 5 stages, rather than over-simplifying it to understanding/not understanding the finality, as I would think that a child old enough to talk fluently can understand simple concepts like life extinguishing of life - that can be a young as age 3. But I would not expect a 3 year old to easily cope with the death of a parent or sister and readily understand they have gone for good.
I have known an 8 year old, upon the death of a pet rabit, to cry and suffer considerable distress - she certainly understood that rabit was gone. But the following day she was fine.
The concepts of life after death, reincarnation, and going to heaven/paradise in almost all major religions indicates that even mature intelligent adults can have difficulty with accepting death as the end - it isn't meraly a matter of consoling the bereaved.
Pure OR, but my nephews started asking about death when they were three, and the elder announced at four he wanted to be a fossil when he died, which let him be okay with the subject. (I had given him a fossil trilobite and explained it was a real animal that had lived very long ago. He concluded that meant it was dead without me having to tell him.) They still ask questions at five and seven but they certainly seem to have realistic views for their ages, despite the scary, pernicious, age-inappropriate, believe-or-you-will-go-to-hell religious comments of one of their grandparents μηδείς (talk) 05:34, 11 January 2013 (UTC).[reply]
Pure OR again: I understood the permanence of the death of an animal (a lamb that I saw die) at the age of 31⁄2. I have only the faintest recollection of the event, but I was subsequently reminded of it several times and thus renewed my memory. I don't think I'd have coped easily with the death of a human at that age -- fortunately no-one close to me died until I was 10, and I can still recall the shock, but I coped because I'd been prepared for the event. I think it also helps if people around you are coping. Dbfirs13:09, 11 January 2013 (UTC)[reply]
Yet more OR. My daughter is ten and has had her family tree pruned repeatedly since her birth. Before three or four, she had no concept that the other person was gone - not sad at the funeral, doesn't ask where they are, has no current memory of them. By around five, she began to worry about her mortality and that of her parents, but it was somewhat disorganized (What happens to my toys if you and mommy die? What do you see when you're dead? How do you know if someone else is dead?) By seven, she had the full response that you'd expect an adult to have: anger, sadness, disappointment, grief, etc. Having gone through it so often, though, I sometimes wonder how much of her grief was just mimicking those around around her to better fit in. For that matter, how would anyone react to death if their culture hadn't already told them how such things get expressed? Matt Deres (talk) 15:01, 11 January 2013 (UTC)[reply]
To keep being able to add pressure at an ever slower rate, but without having to push ever harder? Assume you have access to materials of infinite strength, tensile strength, brittleness, whatever you want. I am just interested in whether in theory you can always convert a reasonable force into increasing pressure. Is the limitation only the materials at hand? --91.120.48.242 (talk) 13:28, 11 January 2013 (UTC)[reply]
Let's suppose you can push your finger on the piston with about 1kPa of pressure (that's like lifting a can of soda with your fingertip) and with a fingertip area of 1 square centimeter. Let's suppose you need to get up to 1000MPa - which is what you'd need to fill your hypothetical pneumatic tank the size of a regular car gas tank and with the capacity of some hypothetical non-liquifying gas that would give your pneumatic car roughly the same range as a regular car.
Well, to get from 1kPa to 1000Mpa - you'd need a million-fold increase in pressure. You suggested to me on my talk page (please don't use that for ref desk-related questions!) that you had in mind some number of pistons connected end to end, each with a cross-sectional area 10x larger than the one before it. So let's go with that - and let's be generous and neglect thinks like leaks and friction and temperature changes and such like. Hence, to get from 1kPa to 1000Mpa, there would need to be six pistons, each 10x thinner in cross-section than the previous one...well, if the low pressure cylinder has the same area as your fingertip (let's say 1cm x 1cm) then the second is ~0.3mm, the third 1mm, then 0.3mm, then 0.1mm, and the last high pressure cylinder would be 0.03mm in diameter. So in pushing that cylinder in a distance that your finger can comfortably move (let's say 5cm?) then pushing on the lowest pressure cylinder once - you'd have produced an amount of compressed gas in the highest pressure cylinder that would be around 5cm long by 0.03mm wide by 0.03mm deep...a total volume of 0.05x0.00003x0.00003 cubic meters. That's 0.000000000045 cubic meters. That's a remarkably small amount of gas!
So to fill your gas-tank-sized container (let's say it's 1/10th of a cubic meter), at a rate of 0.000000000045 cubic meters per push - you'll need to push that first cylinder in and out 2.2 billion times. At one push per second, it would take you about 70 years to fill your tank. If you tried to do it with one pump of a very long cylinder, then the cylinder would be about 7,000 miles long.
You don't get something for nothing...that's the First law of thermodynamics...and it's a fundamental unbreakable law of nature. Because of that, we don't even need to look at the design of some hypothetical machine to tell you that it won't work. It quite simply cannot work - no matter how cleverly you design it because it is a fundamental part of the very fabric of the universe that we live in that "There ain't no such thing as a free lunch"! SteveBaker (talk) 15:10, 11 January 2013 (UTC)[reply]
Steve, thank you - this is a remarkable analysis! Remarkable particularly because of your first paragraph, which correctly summarizes the constraints we're doing away with! You then make very good conclusions logically. But I wonder if you miss the point of the remarkable contraption we now are hypothetically talking about. We goal isn't really to pressurize the gas - it doesn't matter how small the amount of extra volume we add by pushing with 0.1 newtons (which you called 1 kPa over 1cm * 1 cm = https://www.google.com/search?q=1kPa+in+newtons) over 5 cm we get https://www.google.com/q=0.1+newtons+*+5+cm+in+joules 0.005 joules or 0.00138888889 milliwatt hours. If you push the last piston, you get to add 0.005 joules. If you push the next piston directly (using whatever source of torque you want) you get to add 0.05 joules; if you push the next piston down 5 cm you get to add 0.5 joules, and so forth. So, I would say your "70 years" to fill the tank is misleading: you can fill the tank at whatever rate your power source can output torque at! (To the nearest power of ten).
Secondly, I find it very easy to use a finger to push down on a square area that is a lot larger than a single square centimeter: this is my whole point. By making the final area slightly larger, or by playing with the number of differential pumps and their power factors, under the HYPOTHETICAL situation you have first described, can't we continue to fill a gas tank to any point?
Thirdly, when we want that power back OUT again, again under the hypothetical situation we have described, can't we simply open the appropriate valves and let the frictionless pistons (should have mentioned this as well :) push up with whatever force we need, to the nearest power of ten?
Basically, I am asking whether, indeed, this idealized hypothetical solution would not indeed let you store energy by inputing it at whatever torque you want and getting it back out again at whatever torque you want (to the nearest realized piston)? Without (under your hypothetical limits) any constraints other than the weight of the gas and its growing ever hotter as you pump it in?
If you allow yourself to use unobtainium materials with infinite strength, zero elasticity, ignore friction, allow unobtainium infinitely compressible gasses and so forth - then obviously there are all manner of ways to store energy, to input it slowly and extract it slowly - but this is all quite utterly pointless because none of those conditions is even close to being practically realizable.
If you have magical materials then why not build a clockwork car and power it by winding up a giant spring made of unobtainium - or by twisting other unobtainium materials like a rubber band and powering the car like that - or just imagining an ultracapacitor that can store infinite electrical charge - or if you're going to ignore friction and air resistance then a car can be driven any distance (at a constant speed) with no engine at all!
Well, enough - it's trivial to come up with fifty new car power sources that are theoretically viable if you ignore all of the important details. It's all complete B.S though because you're ignoring 100% of the engineering difficulties that make it all quite utterly impossible in practice. Sure, there are theoretical ways to do all sorts of crazy things - but you can't do them for real - so why put so much effort into designing them?
Frankly, your line of questioning has become tiresome - you can't do this, it won't work. Period.
Steve, I apologize. I tried to make it 100% clear from opening with "Imagine a sheet of zero weight and infinite tensile strength" in this question and "Imagine a sheet of zero weight and infinite tensile strength, and you make a container out of this....Basically, I am trying to imagine what happens at the limit of a 'perfect container' for storing compressed air" that I had zero practical interest but was trying to understand something fundamental. The fact that I didn't know a snail is at uniform pressure should also show you that I am not serious but a curious student. I am not very interested in springs, tensile energy storage, vacuum tunnels, supercapacitors or battery technologies at present. This is why I didn't mention them. I wish you would take a slightly better attempt to see the source of my questions, since, in point of fact, compressed air is a currently used form of energy storage. I'm trying to understand it. 178.48.114.143 (talk) 19:00, 11 January 2013 (UTC)[reply]
Exp.SS.4.4.170 - DF1 - MSTN HDR donor candidate 1 - 2 ul Lipofectamine 2000 - 15x - Field 2 - UV red - 2012-12-16.tif
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I would like to merge each "Brightfield" image with its associated "UV red" image using ImageJ. Can anyone help me put together a macro to do this?
I tried using the built-in macro recorder but it doesn't pay attention to how much I increased the contrast of the red images and it also uses specfic file names which is useless when each file is named differently (obviously; you can't have two files with the exact same path!)
129.215.47.59 (talk) 14:23, 11 January 2013 (UTC)[reply]
Resolved
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